Downhole acid stimulation method with corrosion inhibition

ABSTRACT

A method of inhibiting corrosion of metal during acid stimulation of an oil and gas well that involves treating the oil and gas well with an acidic treatment fluid that includes 10 to 28 wt. % of an acid, based on a total weight of the acidic treatment fluid, and a corrosion inhibitor composition containing gelatin, wherein the gelatin is present in the acidic treatment fluid in a concentration of 0.1 to 10% by weight per total volume of the acidic treatment fluid.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTORS

Aspects of this technology are described in an article “Gelatin: A greencorrosion inhibitor for carbon steel in oil well acidizing environment”by K. Haruna, I. B. Obot, N. K. Ankah, A. A. Sorour, and T. A. Saleh, inJournal of Molecular Liquids, 2018, 264, 515-525, which is incorporatedherein by reference in its entirety.

STATEMENT OF ACKNOWLEDGEMENT

The inventors would like to acknowledge the support received from KingAbdulaziz City for Science and Technology (KACST) for funding this workunder the National Science Technology Plan (NSTIP) grant no.14-ADV2448-04. Also, the support provided by the Deanship of ScientificResearch (DSR) and the Center of Research Excellence in Corrosion(CORE-C), at King Fahd University of Petroleum & Minerals (KFUPM) isgratefully acknowledged.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to methods of inhibiting corrosion ofmetal during acid stimulation operations.

Discussion of the Background

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Corrosion is the deterioration of metallic materials by the chemical,electrochemical and metallurgical interaction with its environment. Thecorrosion of steel has very high environmental and economic impact,because of its wide used in many industries. Carbon steel is the mostwidely used material in the construction of oil and gas wells because ofits low cost compared to other materials offering similar physical andchemical properties, but its corrosion resistance is very low. Corrosivesubstances that are present in the crude oil is one source of potentialcorrosion. The annual cost of corrosion in the oil and gas industry isestimated at £1.3 billion. See P. Rajeev, a O. Surendranathan, C. S. N.Murthy, Corrosion mitigation of the oil well steels using organicinhibitors—A review, J. Mater. Environ. Sci. 3 (2012)856-869—incorporated herein by reference in its entirety.

Acidizing of a petroleum oil well is one of the most importantstimulation techniques for improving oil production. Acidizing is usedto enhance oil production by pumping high temperature acid into thewellbore in order create channels in rocks to allow for oil and gas toreach the well and to restore/maximize productivity of old/aging wellsby dissolving rubble and repairing damage found in the old or agingwells. Acids are also employed to remove muds in newly drilled wellsbefore they are used for production. Many different acids are used inacidizing treatments depending on the nature of well and the intendedtreatment, some of which are, hydrochloric acid (HCl), hydrofluoric acid(HF), acetic acid (CH₃COOH), chloroacetic acid (ClCH₃COOH), formic acid(HCOOH) and sulfamic acid (H₂NSO₃H). See A. Singha, M. A. Quraishi,Acidizing corrosion inhibitors: A review, J. Mater. Environ. Sci. 6(2015) 224-235—incorporated herein by reference in its entirety.However, HCl (5-28% W/w) is the most commonly used acid in acidizingtreatment. The technique of acidizing exposes the oil well casing, whichis usually made of carbon steel, to harsh corrosive environments.

The use of corrosion resistant materials, cathodic protection, coatings,and the addition of corrosion inhibitors are the four practical methodsusually employed to control corrosion, with the use of corrosioninhibitors being the most widely used as it has proven to be the mostpractical, economical, and efficient method in protecting oil wellsagainst corrosion. See D. Dwivedi, K. Lepková, T. Becker, Carbon steelcorrosion: a review of key surface properties and characterizationmethods, RSC Adv. 7 (2017) 4580-4610-incorporated herein by reference inits entirety. Inhibitors are added to the acid solution during theacidizing process to reduce the aggressive attack of the acid on oilwells. The effective acidizing inhibitors that are usually found incommercial formulations are acetylenic alcohols, alkenyl phenones,aromatic aldehydes, nitrogen-containing heterocyclics, and condensationproducts of carbonyls and amines. See G. W. Poling, Infrared Studies ofProtective Films Formed by Acetylenic Corrosion Inhibitors, J.Electrochem. Soc. 114 (1967); J. K. D. Neemla, R. C. Saxena, A. K.Agrawal, R. Krishna, Corrosion inhibitor studies on steels inhydrochloric acid, Corros. Prev. Control. 6 (1992) 69-73; W. Frenier, F.Growcock, V. Lopp, α-Alkenylphenones—A New Classof Acid CorrosionInhibitors, CORROSION. 44 (1988) 590-598; M. A. Quraishi, D. Jamal,Dianils: New and Effective Corrosion Inhibitors for Oil-Well Steel(N-80) and Mild Steel in Boiling Hydrochloric Acid, CORROSION, 56 (2000)156-160; T. K. Emranuzzaman, S. Vishwanatham, G. Udayabhanu, Synergisticeffects of formaldehyde and alcoholic extract of plant leaves forprotection of N80 steel in 15% HCl, Corros. Eng. Sci. Technol. 39 (2013)327-332; A. R. S. Priya, V. S. Muralidharan, A. Subramania, Developmentof novel acidizing inhibitors for carbon steel corrosion in 15% boilinghydrochloric acid, CORROSION, 64 (2008) 541-552; and M. Yadav, S. Kumar,P. N. Yadav, Corrosion Inhibition of Tubing Steel during Acidizatiob ofOil and Gas Wells, J. Pet. Eng. 2013 (2013) 9 pages—each incorporatedherein by reference in their entirety. These inhibitors are however,effective only at high concentrations, toxic and not environmentallybenign. See D. D. N. Singh, A. K. Dey, Synergistic Effects of Inorganicand Organic Cations on Inhibitive Performance of Propargyl Alcohol onSteel Dissolution in Boiling Hydrochloric Acid Solution, CORROSION, 49(1993) 594-600—incorporated herein by reference in its entirety.Therefore, the search for new, nontoxic, and environmentally friendlyeffective corrosion inhibitors continues.

Naturally occurring biological compounds have been considered aspossible corrosion inhibitors, most of which are organic compoundscontaining hetero atoms such as nitrogen, sulfur, phosphorus and/oroxygen atoms. See F. Deflorian, I. Felhosi, Electrochemical ImpedanceStudy of Environmentally Friendly Pigments in Organic Coatings,CORROSION 59 (2003) 112-120; S. M. Powell, H. N. McMurray, D. A.Worsley, Use of the Scanning Reference Electrode Technique for theEvaluation of Environmentally Friendly, Nonchromate CorrosionInhibitors, CORROSION, 55 (1999) 1040-1051; M. A. Quraishi, D. Jamal,Technical Note: CAHMT?A New and Eco-Friendly Acidizing CorrosionInhibitor, CORROSION, 56 (2000) 983-985; M. A. Migahed, M. Abd-El-Raouf,A. M. Al-Sabagh, H. M. Abd-El-Bary, Effectiveness of some non-ionicsurfactants as corrosion inhibitors for carbon steel pipelines in oilfields, Electrochim. Acta. 50 (2005) 4683-4689; P. Bommersbach, C.Alemany-Dumont, J. P. Millet, B. Normand, Formation and behaviour studyof an environment-friendly corrosion inhibitor by electrochemicalmethods, Electrochim. Acta. 51 (2005) 1076-1084; T. Zaiz, T. Lanez,Application of some ferrocene derivatives in the field of corrosioninhibition, J. Chem. Pharm. Res. 4 (2012) 2678-2680; G. Blustein, A. R.Di Sarli, J. A. Jaen, R. Romagnoli, B. Del Amo, Study of iron benzoateas a novel steel corrosion inhibitor pigment for protective paint films,Corros. Sci. 49 (2007) 4202-4231; A. Bouyanzer, B. Hammouti, L. Majidi,Pennyroyal oil from Mentha pulegium as corrosion inhibitor for steel in1 M HCl, Mater. Lett. 60 (2006) 2840-2843; M. A. Deyab, Effect ofcationic surfactant and inorganic anions on the electrochemical behaviorof carbon steel in formation water, Corros. Sci. 49 (2007) 2315-2328; A.M. Alsabagh, M. A. Migahed, H. S. Awad, Reactivity of polyesteraliphatic amine surfactants as corrosion inhibitors for carbon steel information water (deep well water), Corros. Sci. 48 (2006) 813-828—eachincorporated herein by reference in their entirety.

Gelatin (FIG. 1 ) is a mixture of proteins and peptides which isproduced by the partial hydrolysis of collagen extracted from the skin,bones, and connective tissues of animals such as domesticated cattle,chicken, pigs, and fish. See N. Devi, M. Sarmah, B. Khatun, T. K. Maji,Encapsulation of active ingredients in polysaccharide-protein complexcoacervates, Adv. Colloid Interface Sci. 239 (2017) 136-145; and S. M.Powell, H. N. McMurray, D. A. Worsley, Use of the Scanning ReferenceElectrode Technique for the Evaluation of Environmentally Friendly,Nonchromate Corrosion Inhibitors, CORROSION, 55 (1999) 1040-1051—eachincorporated herein by reference in their entirety. Gelatin typicallycontains many glycine residues (approximately 1 in every threeresidues), proline and 4-hydroxyl proline residues. See A. Duconseille,T. Astruc, N. Quintana, F. Meersman, V. Sante-Lhoutellier, Gelatinstructure and composition linked to hard capsule dissolution: A review,Food Hydrocoll, 43 (2015) 360-376—incorporated herein by reference inits entirety. Gelatin has been used as green corrosion inhibitor forcorrosion of aluminum copper alloy, alloy steel AISI 304, mild steel,aluminum, and aluminum silicon alloys in mild acids (e.g., 1 M HCl,orthophosphoric acid) and bases (0.1 M NaOH) as cleaning solutions,electropolishing applications, self-healing coatings, etc. See R. B.Patel, J. M. Pandya, K. E. Emtilal, Colloids as corrosion inhibitors foraluminium copper alloy in hydrochloric acid, Proc. Indian Natn. Sci.Acad. 47 A (1981) 555-561; A. Stankiewicz, Z. Jagoda, K. Zielinska, I.Szczygiel, Gelatin microgels as a potential corrosion inhibitor carriersfor self-healing coatings: Preparation and codeposition, Mater. Corros.66 (2015) 1391-1396; W. Goldfarb, Surface active properties of gelatinand their effect on the electropolishing and corrosion behavior of steelin orthophosphoric acid, Egypt. J. Pet. 25 (2016) 229-237; M. Abdallah,E. M. Kamar, A. Y. El-Etre, S. Eid, Gelatin as corrosion inhibitor foraluminum and aluminum silicon alloys in sodium hydroxide solutions,Prot. Met. Phys. Chem. Surfaces. 52 (2016) 140-148; A. Pal, S. Dey, D.Sukul, Effect of temperature on adsorption and corrosion inhibitioncharacteristics of gelatin on mild steel in hydrochloric acid medium,Res. Chem. Intermed. 42 (2016) 4531-4549—each incorporated herein byreference in its entirety.

However, there have been no reports of using gelatin as a corrosioninhibitor in oil field acidizing corrosive environment, i.e., very highconcentration of hydrochloric acids (15% HCl).

In view of the forgoing, there is a need for corrosion inhibitorscompositions that can be used at low concentrations for preventingcorrosion of metal in various oil and gas field environments, includinghigh temperature and highly acidic conditions common to acid stimulationoperations.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the present invention to provide novelmethods of inhibiting corrosion of metal during acid stimulation of anoil and gas well using acidic treatment fluids containing highconcentrations of acids and gelatin as a corrosion inhibitor.

Thus, the present invention provides:

A method of inhibiting corrosion of metal during acid stimulation of anoil and gas well, involving treating the oil and gas well with an acidictreatment fluid comprising 10 to 28 wt.% of an acid, based on a totalweight of the acidic treatment fluid, and a corrosion inhibitorcomposition comprising gelatin, wherein the gelatin is present in theacidic treatment fluid in a concentration of 0.1 to 10% by weight pertotal volume of the acidic treatment fluid.

In some embodiments, the gelatin is present in the acidic treatmentfluid in a concentration of 0.5 to 2.5% by weight per total volume ofthe acidic treatment fluid.

In some embodiments, the gelatin is Type A gelatin derived fromacid-cured porcine skin.

In some embodiments, the gelatin is Type B gelatin derived fromlime-cured bovine skin.

In some embodiments, the gelatin is Type A or Type B gelatin derivedfrom fish skin or fish scales.

In some embodiments, the gelatin has a Bloom number of 50 to less than220.

In some embodiments, the gelatin has a Bloom number of 220 to 325.

In some embodiments, the gelatin has 78 to 80 millimoles of freecarboxyl groups per 100 g of protein.

In some embodiments, the gelatin has 100 to 115 millimoles of freecarboxyl groups per 100 g of protein.

In some embodiments, the corrosion inhibitor composition furthercomprises at least one intensifier selected from the group consisting ofCuI, KI, and formic acid, and wherein the intensifier is present in theacidic treatment fluid in a concentration of 0.001 to 0.15% by weightper total volume of the acidic treatment fluid.

In some embodiments, the intensifier is KI.

In some embodiments, the corrosion inhibitor composition issubstantially free of a cinnamaldehyde compound, an alkoxylated fattyamine, an imidazoline compound, and a carboxylic acid compound having 1to 12 carbon atoms or an ester or salt thereof.

In some embodiments, the corrosion inhibitor composition consists ofgelatin.

In some embodiments, the acidic treatment fluid is substantially free ofa polysaccharide, a synthetic polymer, a quaternary ammonium surfactant,and an organic solvent.

In some embodiments, the acidic treatment fluid is an aqueous solution.

In some embodiments, the acid is HCl and wherein the acidic treatmentfluid comprises 14 to 16 wt. % HCl.

In some embodiments, the oil and gas well is treated with the acidictreatment fluid at a temperature of 25 to 180° C.

In some embodiments, the metal is carbon steel.

In some embodiments, the method has a corrosion inhibition efficiency of55 to 85%.

In some embodiments, the corrosion rate of the metal is from 12 to 36mils penetration per year (mpy).

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 illustrates the chemical structure of gelatin;

FIG. 2 illustrates the X60 carbon steel coupons immediately afterimmersion in 15% HCl solution in the absence and presence of differentconcentrations of gelatin at 25° C.;

FIG. 3 illustrates the X60 carbon steel coupons after 24 h immersion in15% HCl solution in absence and presence of different concentrations ofgelatin at 25° C.;

FIGS. 4A-4C are graphs illustrating (a) Nyquist, (b) Bode plots recordedfor X60 carbon steel in 15% HCl solution in the absence and presence ofdifferent concentrations of gelatin at 25° C. and (c) equivalent circuitmodel used to fit the impedance plots;

FIG. 5 is a graph illustrating the potentiodynamic polarization plotsrecorded for X60 carbon steel in 15% HCl in the absence and presence ofdifferent concentrations of gelatin at 25° C.;

FIGS. 6A-6D illustrate the SEMmicrograph of, (a) X60 carbon steelimmersed in 15% HCl blank after 24 h (b) X60 carbon steel immersed in15% HCl in the presence of 2.5% gelatin after 24 h, (c) X60 carbon steelimmersed in 15% HCl in the presence of gelatin and KI (d) polished X60carbon steel coupon after 24 h;

FIGS. 7A-7D illustrate the EDX spectra of (a) polished X60 carbon steelcoupon (b) X60 carbon steels immersed in 15% HCl blank after 24 h (b)X60 carbon steel immersed in 15% HCl in the presence of 2.5% gelatinafter 24 h, (c) X60 Steel coupon immersed in 15% HCl in the presence ofgelatin and KI;

FIG. 8 is a graph illustrating the FT-IR spectra of (a) solid gelatin,(b) surface-adsorbed layer of the carbon steel immersed in 15% HCl inthe presence of gelatin and (c) surface-adsorbed layer of mild steelimmersed in 15% M HCl in the presence of gelatin and KI;

FIG. 9 is a graph illustrating the UV-Visible spectra of (a) 2.5%gelatin in the 15% HCl recorded prior to immersion of the carbon steel,and (b) solution of 2.5% gelatin in the 15% HCl after 24 h immersion ofthe carbon steel; and

FIG. 10 illustrates a schematic illustration of the adsorption mechanismof gelatin molecules on steel surface in HCl solution.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, it is understood that other embodimentsmay be utilized and structural and operational changes may be madewithout departure from the scope of the present embodiments disclosedherein.

Definitions

As used herein, the term “fatty” describes a compound with a long-chain(linear) hydrophobic portion made up of hydrogen and anywhere from 6 to26, 8 to 24, 10 to 22, 12 to 20, 14 to 18 carbon atoms, which may befully saturated or partially unsaturated, and optionally attached to apolar functional group such as a hydroxyl group, an amine group, or acarboxyl group (e.g., carboxylic acid). Fatty alcohols, fatty amines,fatty acids, fatty esters, and fatty amides are examples of materialswhich contain a fatty portion, and are thus considered “fatty” compoundsherein. For example, stearic acid, which has 18 carbons total (a fattyportion with 17 carbon atoms and 1 carbon atom from the —COOH group), isconsidered to be a fatty acid having 18 carbon atoms herein.

As used herein, “alkoxylated” or “alkoxylate” refers to compoundscontaining a (poly)ether group (i.e., (poly)oxyalkylene group) derivedfrom reaction with, oligomerization of, or polymerization of one or morealkylene oxides having 2 to 4 carbon atoms, and specifically includes(poly)oxyethylene (derived from ethylene oxide, EO), (poly)oxypropylene(derived from propylene oxide, PO), and (poly)oxybutylene (derived frombutylene oxide, BO), as well as mixtures thereof.

The phrase “substantially free”, unless otherwise specified, describes aparticular component being present in an amount of less than about 1 wt.%, preferably less than about 0.5 wt. %, more preferably less than about0.1 wt. %, even more preferably less than about 0.05 wt. %, yet evenmore preferably 0 wt. %, relative to a total weight of the compositionbeing discussed.

As used herein, the terms “optional” or “optionally” means that thesubsequently described event(s) can or cannot occur or the subsequentlydescribed component(s) may or may not be present (e.g., 0 wt. %).

The term “alkyl”, as used herein, unless otherwise specified, refers toa straight, branched, or cyclic, aliphatic fragment having 1 to 26carbon atoms, preferably 8 to 22, and more preferably 12 to 18.Non-limiting examples include, but are not limited to, methyl, ethyl,propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl,neopentyl, hexyl, isohexyl, 3-methylpentyl, 2,2-dimethylbutyl,2,3-dimethylbutyl, lauryl, myristyl, cetyl, stearyl, and the like,including guerbet-type alkyl groups (e.g., 2-methylpentyl, 2-ethylhexyl,2-proylheptyl, 2-butyloctyl, 2-pentylnonyl, 2-hexyldecyl,2-heptylundecyl, 2-octyldodecyl, 2-nonyltridecyl, 2-decyltetradecyl, and2-undecylpentadecyl), and unsaturated alkenyl and alkynyl variants suchas vinyl, allyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl,3-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl,2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, oleyl, linoleyl, and thelike. Cycloalkyl is a type of cyclized alkyl group. Exemplary cycloalkylgroups include, but are not limited to, cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, norbornyl, and adamantyl. The term “loweralkyl” is used herein to describe alkyl groups having 1 to 5 carbonatoms (e.g., methyl, ethyl, n-propyl, etc.).

As used herein, unless otherwise specified, the term “aryl” refers to anaromatic group containing only carbon in the aromatic ring(s), such asphenyl, biphenyl, naphthyl, anthracenyl, and the like. The term“heteroarene” or “heteroaryl” refers to an arene compound or aryl groupwhere at least one carbon atom is replaced with a heteroatom (e.g.,nitrogen, oxygen, sulfur) and includes, but is not limited to, pyridine,pyrimidine, quinoline, isoquinoline, pyrazine, pyridazine, indole,pyrrole, oxazole, furan, benzofuran, thiophene, benzothiophene,isoxazole, pyrazole, triazole, tetrazole, indazole, purine, carbazole,imidazole, and benzimidazole.

“Aroyl” refers to aryl carbonyl (arylC(O)—) substituents, such asbenzoyl and naphthoyl while “alkanoyl” refers to alkyl variants(alkylC(O)—), where the alkyl group is bound to a carbon that isattached to an oxygen atom through a double bond. Examples of alkanoylsubstitution includes, acetyl, propionyl, butyryl, isobutyryl, pivaloyl,valeryl, hexanoyl, octanoyl, lauroyl, and stearoyl. As used herein,“alkanoyloxy” groups are alkanoyl groups that are bound to oxygen(—O—C(O)-alkyl), for example, acetyloxy, propionyloxy, butyryloxy,isobutyryloxy, pivaloyloxy, valeryloxy, hexanoyloxy, octanoyloxy,lauroyloxy, and stearoyloxy. “Alkoxycarbonyl” substituents are alkoxygroups bound to C═O (e.g. —C(O)—Oalkyl), for example methyl ester, ethylester, and pivaloyl ester substitution where the carbonyl functionalityis bound to the rest of the compound.

As used herein, “optionally substituted” means that at least onehydrogen atom is replaced with a non-hydrogen group, provided thatnormal valencies are maintained and that the substitution results in astable compound. Such optional substituents may include, but are notlimited to, aryl, alkoxy, aryloxy, arylalkyloxy, aroyl, alkanoyl,alkanoyloxy, carboxy, alkoxycarbonyl, hydroxy, halo (e.g. chlorine,bromine, fluorine or iodine), amino (e.g. alkylamino, arylamino,arylalkylamino, alkanoylamino, either mono- or disubstituted), oxo,amido (e.g. —CONH₂, —CONHalkyl, —CONHaryl, —CONHarylalkyl or cases wherethere are two substituents on one nitrogen), and the like.

As used herein the term “corrosion inhibitor” refers to a substance(s)that prevents or reduces the deterioration of a metal surface byoxidation or other chemical reaction. Corrosive substances that cancause corrosion, particularly of metal surfaces of equipment used duringstimulation operations, include water with high salt contents, acidicinorganic compounds such as hydrochloric acid, hydrofluoric acid, carbondioxide (CO₂) and/or hydrogen sulfide (H₂S), organic acids, andmicroorganisms. Preferred corrosion inhibitor compositions of thepresent invention reduce, inhibit and/or prevent the destructive effectsuch substances have on various metal surfaces.

As used herein, the phrase “acid stimulation” or “acidizing” refers tothe general process of introducing an acidic fluid downhole to performat least one of the following functions: (1) to react with and todissolve the area surrounding the well which has been damaged; (2) toreact with and to dissolve rock associated with the geological formationto create small conducting channels (e.g., conducting wormholes) throughwhich the hydrocarbon will flow; and (3) to create a large flow channelby injecting acidic fluids through the well at pressures sufficient tofracture the rock, thus allowing the hydrocarbon to migrate rapidly fromthe rock to the well. Thus, “acid stimulation” or “acidizing” may referto either or both matrix acidizing and fracture acidizing treatments.

Methods of Inhibiting Corrosion

Petroleum oil and natural gas wells are typically subjected to numerouschemical treatments during their production life to enhance operationand protect the integrity of the well and all related equipment. Acidicfluids (HCl, HF, etc.) are often used in stimulation operations such asin matrix acidizing and fracture acidizing treatments, where acidicfluids are injected into the well penetrating the rock pores tostimulate the well to improve flow or to remove damage. In matrixacidizing treatments, acidic treatment fluids are either injected intothe well to react with and to dissolve the area surrounding the well toremove damage around the wellbore, or introduced into the subterraneanformation under pressure (but below the fracture pressure) so that theacidic treatment fluids flow into the pore spaces of the formation andreact with acid-soluble materials contained in the formation, resultingin an increase in the size of the pore spaces and an increase in thepermeability of the formation. In fracture-acidizing treatments, theacidic treatment fluids are introduced above the fracture point of theformation to etch flow channels in the fracture face of the formationand to enlarge the pore spaces in the formation. The increase information permeability from these types of acidic treatments mayincrease the recovery of hydrocarbons from the formation. In most cases,acid stimulation procedures are carried out in calcareous formationssuch as dolomites, limestones, dolomitic sandstones, and the like.

A common problem associated with using acidic treatment fluids insubterranean formations is the corrosion of metal surfaces in piping,tubing, heat exchangers, reactors, downhole tools, and the otherequipment which are exposed to such acid treatments. Further, othercorrosive components such as brines, carbon dioxide, hydrogen sulfide,and microorganisms, may be entrained within the acidic stimulationfluids during stimulation, exacerbating the corrosion problem. Moreover,elevated temperatures are commonly encountered in deeper formationswhich increases the rate of corrosion. Corrosion issues are problematicfor any drilling operation, but are even more troublesome in deep-seaoperations where replacement of corroded equipment is difficult andcostly.

Therefore, it is common practice to employ corrosion inhibitors duringacid stimulation treatments of crude oil and natural gas wells. However,many corrosion inhibitors suffer from poor performance at lowconcentrations and particularly poor performance under high temperaturesand under strongly acidic solutions, for example acidic solutionscontaining greater than or equal to 15 wt. % acid, necessitating theneed for large quantities of corrosion inhibitors to be used. The use oflarge quantities of corrosion inhibitors is extremely undesirable whensynthetic corrosion inhibitors are deployed in terms of both cost andfrom environmental concerns.

The present disclosure thus provides a method for inhibiting corrosionduring acid stimulation in an oil and gas field using corrosioninhibitors obtained from natural sources. The methods involve treatingor otherwise introducing an acidic treatment fluid containing an acidand a corrosion inhibitor composition comprising, consisting essentiallyof, or consisting of gelatin into an oil and gas well.

Acidic Treatment Fluid

The acidic treatment fluid of the present disclosure generally containsan acid and a corrosion inhibitor composition. The acidic treatmentfluid may optionally include one or more of a surfactant, an organicsolvent, and an additive.

Acid The acid treatment fluid may contain a variety of acids, preferablywater-soluble acids. Suitable acids include, but are not limited to,hydrochloric acid, formic acid, acetic acid, chloroacetic acid,hydrofluoric acid, sulfuric acid, sulfamic acid, as well as mixturesthereof, for example mud acid (mixtures of HCl and HF). In preferredembodiments, the acid is hydrochloric acid (HCl). Typically, the acidictreatment fluid contains 5 to 28 wt. % of the acid, preferably 7 to 24wt. % of the acid, preferably 9 to 22 wt. % of the acid, preferably 10to 20 wt. % of the acid, preferably 12 to 18 wt. % of the acid,preferably 14 to 16 wt. % of the acid(s) (e.g., HCl), based on a totalweight of the acidic treatment fluid, although more concentrated (e.g.,about 37 wt. %) or dilute versions may also be used in somecircumstances. In some embodiments, the acidic treatment fluid has a pHof less than 3, preferably less than 2, preferably less than 1,preferably less than 0, for example from −2 to 0, or from −1 to 0.

In some embodiments, when the acidic treatment fluids are employed inthe acid stimulation methods of the present disclosure, formationchemicals and fluids may become entrained therein. Therefore, inaddition to the acid(s) listed above, the acidic treatment fluids mayalso contain other corrosive agents, including, but not limited to,carbon dioxide, corrosive sulfur species (e.g., hydrogen sulfide,mercaptans, etc.), brine, as well as mixtures thereof.

In preferred embodiments, the acidic treatment fluid is an aqueoussolution, i.e., is substantially free of an oil phase. Preferably, theacidic treatment fluid is injected into the oil and gas well as anaqueous solution for acid stimulation operations, and in doing so, onlyminor amounts of produced oil and gas from the geological formation isentrained therein. However, the acidic treatment fluids may be effectivefor acid stimulation operations and simultaneously inhibiting corrosionof metal when in the form of multi-phase mixtures (e.g., water-oilmixtures and water-oil-gas mixtures), and emulsions. When in the form ofmulti-phase mixtures or emulsions, the acidic treatment fluid ispreferably aqueous-based (in the case of emulsions, the aqueous phase ispreferably the continuous phase).

Corrosion Inhibitor Compositions

The present disclosure provides corrosion inhibitor compositions thatgenerally include gelatin and optionally one or more of an intensifierand a secondary corrosion inhibitor.

Gelatin

Gelatin (or gelatine) is a mixture of proteins and peptides (FIG. 1 )which is produced by the partial hydrolysis (breakdown) of collagenextracted from the skin, bones, and/or connective tissues of animalssuch as domesticated cattle, chicken, pigs, and marine sources, inparticular, bovine bones and hide, porcine skin, fish skin/scales, orfish offal. Gelatin is typically composed of approximately 86% protein,12% moisture, and 2% ash (minerals) by weight, with the protein contentbeing a heterogeneous mixture of water-soluble proteins of highmolecular weight, typically containing many glycine residues(approximately 1 in every three residues), proline, and4-hydroxylproline residues.

Broadly speaking, there are two types of gelatin, Type A gelatin andType B gelatin, depending on the method of extraction, with each typehaving distinct structure and properties despite the fact they may beobtained from the exact same source. Type A gelatin is derived fromacid-cured tissue and Type B gelatin is derived from lime-cured tissue.

In one illustrative example, Type A gelatin may be produced according tothe following procedure (See U.S. Pat. No. 9,132,112B2; Sebastian, M.“Industrial Gelatin Manufacture—Theory and Practice” Academia, 2014—eachincorporated herein by reference in its entirety). The animal skins(e.g., pigskins) may be dehaired and degreased and then passed through achopper or macerator to cut the skin into uniform sizes. The skin maythen be soaked/swelled at a pH of 1 to 4 with a food-grade mineral acidsuch as hydrochloric acid, phosphoric acid or sulfuric acid (e.g., 1 to5% w/w acid solutions) for 8 to 30 hours, preferably 10 to 28 hours,preferably 12 to 26 hours, preferably 14 to 24 hours. The acid-treatedskin (e.g., pigskin) may then be washed with water to remove impuritiesand extracted with hot water, usually in four to five extractions. Thefour to five extractions are typically made at temperatures increasingfrom 55 to 65° C. for the first extract to 95 to 100° C. for the lastextract. Each extraction lasts about 4-8 hours. The extract may bedegreased and filtered through an anion-cation exchange column to reduceash or mineral levels. The gelatin extract may be vacuum concentrated orultra-filtered to a concentration between 15 to 35%, preferably 20 to30%, preferably 22 to 28%, preferably 24 to 26% by weight, filtered, andthe pH may be adjusted to between 3.5 and 6, preferably between 4 and5.5, preferably between 4.5 and 5, and evaporated to 40 to 60%,preferably about 50% solids by weight. The residue may be chilled,extruded, dried, and milled to a preferred particle size and thenpackaged. It is also known to pre-treat bovine ossein (de-mineralisedbone) with acid prior to extraction of the gelatin although bovineossein is more commonly pre-treated with alkali.

In another illustrative example, Type B gelatin may be producedaccording to the following procedure (See U.S. Pat. No. 9,132,112B2;Sebastian, M. “Industrial Gelatin Manufacture—Theory and Practice”Academia, 2014—each incorporated herein by reference in its entirety).Type B gelatin is made mostly from bovine bones, but may also be madefrom bovine hides and pork skins. The bones for type B gelatin may becrushed and optionally cooked, centrifuged and dried, and then degreasedat a rendering facility. Rendered bone pieces, typically of 0.5 to 4 cmsize and with less than 3%, preferably less than 2%, preferably lessthan 1% fat by weight, may be treated with cool, 4 to 7%, preferably 5to 6% hydrochloric acid (w/w) for 4 to 14, preferably 5 to 12,preferably 6 to 10, preferably 7 to 8 days to remove the mineralcontent. The demineralized bones (i.e., ossein), may then be washed andtransferred to large tanks where they are stored in a lime slurry,typically a 1 to 4%, preferably 2 to 3% lime (calcium hydroxide) slurryby weight, to adjust the pH to 10 to 13, or about 12. The ossein may bestored in such slurry tanks for 3 to 16 weeks, preferably 4 to 14 weeks,preferably 5 to 12 weeks, with daily agitation and weekly lime changesto remove non-collagen components. During the liming process, somedeamination of the collagen may occur with evolution of ammonia(resulting in low isoelectric ranges for type B gelatin). After washingfor 15 to 30 hours, preferably 18 to 28 hours, preferably 20 to 26 hoursto remove the lime, the ossein may be acidified to pH 3 to 7, preferably4 to 6, preferably about with an appropriate acid. Then the extractionprocessing for Type A gelatin described above is commonly followed.While the above description relates to bovine bone, bovine hides andskins are also substantial sources of raw material for Type B gelatinand are supplied in the form of splits, trimmings of dehaired hide,rawhide pieces or salted hide pieces. Like pork skins, the hides areoften cut to smaller pieces before being processed. The liming of hidesusually takes a little longer than the liming of ossein from bone.

For marine (e.g., fish skin) processing to form Type A gelatin, theskins, scales, or offal of fish may be optionally pre-treated withdilute alkali for 18 to 24 hours, preferably 20 to 22 hours, and thenwashed and treated with dilute mineral acid, preferably sulfuric acid.The acid-treated material may then be optionally washed with water,treating with dilute aqueous organic acid, washed again with water, andextracted with water at elevated temperatures of 40 to 50° C., but below55° C., to yield the gelatin product (See GB 235,635; EP 0436266; U.S.Pat. No. 5,194,282—each incorporated herein by reference in itsentirety). Another Type A gelatin-producing process is describedEP1016347A1—incorporated herein by reference in its entirety, whichinvolves washing the raw fish skins with water containing oxidizingagents, such as sodium hypochlorite or hydrogen peroxide, beforeextracting the washed and acid-treated skins at an acidic pH (noalkaline conditioning step is used in this process).

Type B gelatin from marine sources may be produced by the processdescribed in U.S. Pat. No. 5,484,888—incorporated herein by reference inits entirety, in which fish skins are soaked in an alkaline solution for60 days and then the excess alkali is removed before extracting thegelatin from an alkaline solution (see also WO2002094959A1—incorporatedherein by reference in its entirety).

The content of amino acids found in gelatins varies depending on theanimal source and the method of extraction, that is Type A versus Type Bgelatin. For example, Table A below provides a comparison of the aminoacid content of various gelatins obtained by complete hydrolysis, ingrams of amino acid per 100 grams dry gelatin (GMIA 2019. GelatinHandbook. Gelatin Manufactures Institute of America (USA: GMIA), pg.1-27−incorporated herein by reference in its entirety).

TABLE A Example amino acid composition of various gelatins Type A Type BType B (Porkskin) (Calf Skin) (Bone) Alanine 8.6 10.7 9.3 11.0 10.1 14.2Arginine 8.3 9.1 8.55 8.8 5.0 9.0 Aspartic Acid 6.2 6.7 6.6 6.9 4.6 6.7Cystine 0.1 Trace Trace Glutamic Acid 11.3 11.7 11.1 11.4 8.5 11.6Glycine 26.4 30.5 26.9 27.5 24.5 28.8 Histidine 0.9 1.0 0.74 0.8 0.4 0.7Hydroxylysine 1.0 0.91 1.2 0.7 0.9 Hydroxyproline 13.5 14.0 14.5 11.913.4 Isoleucine 1.4 1.7 1.8 1.3 1.5 Leucine 3.1 3.3 3.1 3.4 2.8 3.5Lysine 4.1 5.2 4.5 4.6 2.1 4.4 Methionine 0.8 0.9 0.8 0.9 0.0 0.6Phenylalanine 2.1 2.6 2.2 2.5 1.3 2.5 Proline 16.2 18.0 14.8 16.4 13.515.5 Serine 2.9 4.1 3.2 4.2 3.4 3.8 Threonine 2.2 2.2 2.0 2.4 Tyrosine0.4 0.9 0.2 1.0 0.0 0.2 Valine 2.5 2.8 2.6 3.4 2.4 3.0

The differences between Type A and Type B gelatin may also be measuredaccording to carboxyl group content, with Type A gelatin typicallyhaving 78 to 80 millimoles of free carboxyl groups per 100 g of protein,and Type B gelatin typically having 100 tol 15 millimoles of freecarboxyl groups per 100 g of protein.

The different constitutional makeup (e.g., varying amino acid content)of gelatins depending on sources and processing types can impact theproperties of the gelatin, for example, its propensity to gel, the gelstrength (Bloom), the viscosity, and the isoelectric point, all of whichmay affect the gelatin's ability to adsorb onto metal surfaces forinhibiting corrosion.

The gelatin used in the present disclosure may be extracted from anumber of sources of collagen, the most preferred being bovine bones andhide, porcine skin, or fish skin or scales. In preferred embodiments,the gelatin is derived from porcine skin or bovine skin. In someembodiments, the gelatin is derived from a mixture of collagen sources,for example, from a mixture of porcine and bovine collagen.

In some embodiments, the gelatin used herein is Type A gelatin,preferably Type A gelatin derived from acid-cured porcine skin. In someembodiments, the gelatin is Type B gelatin, preferably Type B gelatinderived from lime-cured bovine skin. In some embodiments, the gelatin isType A gelatin derived from fish skin or fish scales. In someembodiments, the gelatin is Type B gelatin derived from fish skin orfish scales. In some embodiments, the gelatin used herein is a mixtureof Type A and Type B gelatin.

In terms of its basic elements, the gelatin used in the disclosedmethods is preferably composed of 49 to 52%, preferably 50 to 51%,preferably about 50.5% carbon; 5 to 8%, preferably 6 to 7%, preferablyabout 6.8% hydrogen; 15 to 19%, preferably 16 to 18, preferably about17% nitrogen; and 24 to 27%, preferably 25 to 26%, preferably about25.2% oxygen.

In some embodiments, the gelatin has 78 to 80, preferably 79 millimolesof free carboxyl groups per 100 g of protein. In some embodiments, thegelatin has 100 to 115, preferably 105 to 110, preferably about 108millimoles of free carboxyl groups per 100 g of protein.

Gelatin has the ability to form thermo-reversible gels, and the gelstrength of gelatin can be assessed using the Bloom gel strength test,which is a standard test procedure from the Gelatin ManufacturesInstitute of America (Standard Methods for the Sampling and Testing ofGelatins, Gelatin Manufacturers Institute of America, Inc., 1986, 501fifth Ave. New York, N.Y., as well as The Association of AnalyticalCommunities (AOAC) international, AOAC method 948.21 “Jelly Strength ofGelatin”—each incorporated herein by reference in its entirety). TheBloom number is the force (in grams) required to depress a standard AOACplunger (12.7 mm diameter flat face cylindrical probe with a sharp edge)4 mm into a set gelatin of 6.66% (w/v) concentration (e.g., 7.5 ggelatin in 105 mL of water) that has been kept at 10° C. for 16 hours.This gelling ability is related to both the average molecular weight ofthe gelatin and to the content of the hydroxyproline and proline aminoacids in the collagen used. The gelatin of the present disclosure may becategorized according to the following Bloom number categories: <50(very low bloom); 50 to <150 (low bloom); 150 to <220 (medium bloom);220 to 325 (high bloom).

In some embodiments, the gelatin is a very low Bloom gelatin, having aBloom number of less than 50, preferably less than 40, preferably lessthan 30, preferably less than 20. In some embodiments, the gelatin is alow Bloom gelatin, having a Bloom number of 50 to less than 150,preferably 75 to 125, preferably 90 to 110. In some embodiments, thegelatin is a medium Bloom gelatin, having a Bloom number of 150 to lessthan 220, preferably 160 to 210, preferably 175 to 200. In someembodiments, the gelatin is a high Bloom gelatin, having a Bloom numberof 220 to 325, preferably 225 to 300, preferably 250 to 290, preferably275 to 280.

The gelatin employed in the disclosed methods may have a viscositybetween 1.5 to 7.89 mPas, preferably 2 to 7 mPas, preferably 2.5 to 6.5mPas, preferably 3 to 6 mPas, preferably 3.5 to 5.5 mPas, preferably 4to 5 mPas, preferably 4.3 to 4.7 mPas, as determined using the GelatinManufactures Institute of America standard procedure (Standard Methodsfor the Sampling and Testing of Gelatins, Gelatin ManufacturersInstitute of America, Inc., 1986, 501 fifth Ave. New York, N.Y. testingstandard (6.66% w/v concentration at 60° C. using a calibrated glasscapillary viscometer). In some embodiments, the gelatin is Type Agelatin with a viscosity of 2.7 to 4.2 mPas, preferably 3 to 4 mPas,preferably 3.2 to 3.8 mPas. In some embodiments, the gelatin is a Type Bgelatin with a viscosity of 3.6 to 4.2 mPas, preferably 3.8 to 4.1 mPas,preferably 3.9 to 4 mPas. In some embodiments, the gelatin is a porcineskin gelatin or a grass carp gelatin with a viscosity of 7 to 7.89 mPas,preferably 7.07 to 7.8 mPas, preferably 7.2 to 7.6 mPas.

In some embodiments, the gelatin employed herein is a Type A gelatinhaving a pH as a 1.5% (w/v) solution at 25° C. of 3.8 to 5.5, preferably4 to 5.2, preferably 4.2 to 5, preferably 4.4 to 4.8. In someembodiments, the gelatin employed herein is a Type B gelatin having a pHas a 1.5% (w/v) solution at 25° C. of 5 to 7.5, preferably 5.2 to 7,preferably 5.4 to 6.8, preferably 5.6 to 6.6.

Another property of gelatin that may influence its ability to adsorbonto metal surfaces and thus act as a corrosion inhibitor is itsisoelectric point. The isoelectric point is the pH at which the gelatinmolecule carries no net electrical charge or is electrically neutral inthe statistical mean, and thereby shows no net migration on applicationof an electric field. In some embodiments, the gelatins of the presentdisclosure have an isoelectric point (pI) of 4.7 to 5.4, preferably 4.8to 5.3, preferably 4.9 to 5.2, preferably 5 to 5.1, for example for TypeB gelatins. In some embodiments, the gelatins of the present disclosurehave an isoelectric point (pI) of 6.3 to 9.2, preferably 6.5 to 9,preferably 6.8 to 8.6, preferably 7 to 8.2, for example for Type Agelatins.

In addition to gelatins produced by the partial collagen hydrolysismethods described above (e.g., Type A and Type B gelatins), modifiedgelatins are also contemplated for use in the present disclosure.Acceptable examples of modified gelatins include, but are not limitedto, enzyme modified gelatins such as gelatins treated withtransglutaminase, polyphenol oxidases, and the like, to formcross-linked gelatins; (meth)acrylamide modified gelatins subject toradical crosslinking, such as those described in U.S. Pat. No.6,458,386B1—incorporated herein by reference in its entirety;alkoxylated gelatins such as those described in U.S. Pat. No.4,195,077A—incorporated herein by reference in its entirety; andrecombinant gelatin such as the recombinant gelatins described in U.S.Pat. No. 7,393,928B2—incorporated herein by reference in its entirety.

Gelatin may be used in any amount sufficient to provide a desiredanticorrosive effect. Typically, and in preferred embodiments, thegelatin is present in the acidic treatment fluid in a concentration of0.01 to 10%, preferably 0.1 to 9.8%, preferably 0.2 to 9.5%, preferably0.3 to 9%, preferably 0.4 to 8.5%, preferably 0.5 to 8%, preferably 0.8to 7.5%, preferably 1 to 7%, preferably 1.2 to 6.5%, preferably 1.5 to6%, preferably 1.8 to 5.5%, preferably 2.0 to 5%, preferably 2.5 to4.5%, by weight per total volume of the acidic treatment fluid. Ofcourse, gelatin dosages above or below these values may be used in somecircumstances, when appropriate.

In some embodiments, the corrosion inhibitor composition consists ofgelatin. In other words, gelatin may be the only corrosion inhibitorpresent in the acidic treatment fluid.

Intensifier

In some situations, for example, under particularly harsh conditions,the corrosion inhibitor compositions may optionally further include oneor more intensifiers to further diminish the rate of corrosion. Suitableintensifiers may include, but are not limited to,

-   -   carboxylic acid compounds having 1 to 12 carbon atoms or an        ester (including protected carboxylic acid derivatives) or salt        thereof, such as formic acid, acetic acid, oxalic acid, glycolic        acid, propionic acids/esters/salts (e.g., propionic acid,        2-hydroxypropionic acid, 3-hydroxypropionic acid,        2-methoxypropionic acid, 3-methoxypropionic acid,        2-hydroxypropionic acid methyl ester, 3-hydroxypropionic acid        methyl ester, 2-methoxypropionic acid methyl ester,        3-methoxypropionic acid methyl ester, sodium        2-hydroxypropionate, sodium 3-hydroxypropionate, sodium        2-methoxypropionate, and sodium 3-methoxypropionate), lactic        acid, butanoic acid, isobutyric acid, pentanoic acid, arabinaric        acid, glucaric acid, tartaric acid, 1,1-cyclobutanedicarboxylic        acid, 2-(2-propynyl)malonic acid, 2,2-bis(hydroxymethyl)butanoic        acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-diethylmalonic        acid, 2,2-dihydroxymalonic acid hydrate,        2,2-dimethyl-1,3-dioxane-4,6-dione, 2,2-dimethylmalonic acid,        2-allylmalonic acid, 2-amino-2,4,5-trideoxypentonic acid,        2-butylmalonic acid, 2-ethylmalonic acid,        2-hydroxy-2-methylsuccinic acid, 2-isopropylmalonic acid,        2-methylmalonic acid, 2-methylserine, 3-(acryloyloxy)propanoic        acid, 3-ethoxy-2-methyl-3-oxopropanoic acid, 3-ethoxypropanoic        acid, 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid,        3-hydroxy-2,2-dimethylpropanoic acid, 3-hydroxy-2-oxopropanoic        acid, 3-hydroxy-3-methylbutanoic acid, 3-hydroxybutanoic acid,        3-hydroxyproline, 3-methoxy-2-methyl-3-oxopropanoic acid,        3-methoxy-3-oxopropanoic acid, 3-methoxyalanine,        3-methoxybutanoic acid, 3-methoxypropanoic acid,        3-methoxyvaline, 4-amino-3-hydroxybutanoic acid,        4-hydroxy-4-methyltetrahydro-2H-pyran-2-one,        4-methyl-5-oxotetrahydro-3-furancarboxylic acid, diethyl        malonate, dimethyl 2-ethylidenemalonate, dimethyl        2-methylmalonate, dimethyl malonate, disodium malonate, ethyl        3-ethoxypropanoate, ethyl 3-hydroxybutanoate,        hydroxydihydro-2(3H)-furanone, lithium        3-hydroxy-2-oxopropanoate, malic acid, malonic acid, methyl        2-(1-hydroxyethyl)acrylate, methyl 2-amino-3-hydroxybutanoate,        methyl 2-amino-3-hydroxypropanoate hydrochloride, methyl        2-oxo-2H-pyran-3-carboxylate, methyl 3, 3-dimethoxypropanoate,        methyl 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoate, methyl        3-hydroxy-2, 2-dimethylpropanoate, methyl 3-hydroxyhexanoate,        methyl 3-methoxypropanoate, N-acetylserine, potassium        3-methoxy-3-oxopropanoate, serine, sodium 3-hydroxybutanoate,        sodium malonate dibasic monohydrate, tartronic acid, and        threonine, for example, those carboxylic        acids/esters/salts/protected derivatives described in WO        2007007025 A1—incorporated herein by reference in its entirety;    -   formates such as C₁-C₄ alkyl formates (e.g., methyl formate and        ethyl formate), aryl formates, and arylalkyl formates (e.g.,        benzyl formate);    -   formamides such as formamide, dimethyl formamide, 1,        1′-azobisformanide;    -   metal halides such as sodium bromide, potassium bromide, sodium        iodide, potassium iodide, copper(I) chloride, copper(I) iodide,        copper(II) chloride, copper(II) iodide, antimony chloride;    -   as well as combinations thereof.

When employed, the intensifier is preferably at least one selected fromthe group consisting of CuI, KI, and formic acid, more preferably KI.

The intensifier may be pre-mixed with gelatin as part of the corrosioninhibitor composition, and may be introduced into the oil and gas welltogether in the acidic treatment fluid, or alternatively, theintensifier may be added to the oil and gas well as a separate componentand the corrosion inhibitor composition may be formed downhole.

When employed, the intensifier may be present in a concentration of0.001 to 3%, preferably 0.005 to 1%, preferably 0.01 to 0.5%, preferably0.05 to 0.15%, preferably 0.08 to 0.10% by weight per total volume ofthe acidic treatment fluid.

In preferred embodiments, the corrosion inhibitor composition (and thusthe acidic treatment fluid) is substantially free of an intensifier. Inpreferred embodiments, the corrosion inhibitor composition (and thus theacidic treatment fluid) is substantially free of a carboxylic acidcompounds having 1 to 12 carbon atoms or an ester or salt or protectedcarboxylic acid derivative thereof, and metal halides (e.g., CuI, KI).

Secondary Corrosion Inhibitor

The corrosion inhibitor compositions may also optionally include one ormore secondary corrosion inhibitors (in addition to gelatin). Suitablesecondary corrosion inhibitors include, but are not limited to, acinnamaldehyde compound, an alkoxylated fatty amine, and an imidazolinecompound. When used, the secondary corrosion inhibitor may be present inamounts of 0.01 to 20%, preferably 0.05 to 15%, preferably 0.1 to 10%,preferably 0.5 to 5%, preferably 1 to 2% by weight per total volume ofthe acidic treatment fluid.

The cinnamaldehyde compound generally contains an optionally substitutedaryl group separated from an aldehyde moiety (or a functional groupmimic, protecting group, or isostere thereof) by one unsaturatedcarbon-carbon double bond or a two or more unsaturated carbon-carbondouble bonds in conjugation (i.e., polyene moiety), the simplest ofwhich is cinnamaldehyde (i.e., 3-phenyl-2-propen-1-al, C₆H₅CH═CHCHO),which may be obtained naturally from cinnamon oil. The aryl group may beunsubstituted (contain only hydrogen as is the case in cinnamaldehyde)or may be substituted with up to 5 substituents individually selectedfrom the group consisting of an optionally substituted alkyl, anoptionally substituted aryl, an optionally substituted alkoxy, anoptionally substituted aroyl, an optionally substituted alkanoyl, anoptionally substituted alkanoyloxy, a carboxy, an optionally substitutedalkoxycarbonyl, a hydroxy, a halo, an amino group of the formula —NH₂,—NHR_(a), or —N(R_(a))₂, an alkyl ammonium salt of the formula—(N(R_(a))₃)⁺, a nitro, a cyano, a sulfate anion, an alkylsulfate, athiocyano, an optionally substituted alkylthio, an optionallysubstituted alkylsulfonyl, an optionally substituted arylsulfonyl, or anoptionally substituted sulfonamido (e.g., —SO₂NH₂), or wherein twoadjacent substituents together form a methylene dioxy group. Examples ofcinnamaldehyde compounds that can be used herein include, but are notlimited to, cinnamaldehyde, 3,3′-(1,4-phenylene)diacrylaldehyde,p-hydroxycinnamaldehyde, p-methylcinnamaldehyde, p-ethylcinnamaldehyde,p-methoxycinnamaldehyde, 2,4,5-trimethoxycinnamaldehyde,3,4,5-trimethoxycinnamaldehyde, 3,4-dimethoxycinnamaldehyde,1-ethoxy-2-acetoxycinnamaldehyde, 1-ethoxy-2-hydroxycinnamaldehyde,sinapaldehyde, 2,5-dimethoxy-3,4-methylenedioxycinnamaldehyde,2-methoxy-4,5-methylenedioxy cinnamaldehyde, coniferyl aldehyde,2,3-dimethoxy-4,5-methylenedioxycinnamaldehyde,p-dimethylaminocinnamaldehyde, p-diethylaminocinnamaldehyde,p-nitrocinnamaldehyde, o-nitrocinnamaldehyde,3,4-methylenedioxycinnamaldehyde, sodium p-sulfocinnamaldehyde,p-trimethylammoniumcinnamaldehyde sulfate,p-trimethylammoniumcinnamaldehyde o-methylsulfate,p-thiocyanocinnamaldehyde, p-chlorocinnamaldehyde,a-methylcinnamaldehyde, B-methylcinnamaldehyde, a-chlorocinnamaldehyde,a-bromocinnamaldehyde, a-butylcinnamaldehyde, a-amylcinnamaldehyde,a-hexylcinnamaldehyde, a-bromo-p-cyanocinnamaldehyde,a-ethyl-p-methylcinnamaldehyde, and p-methyl-a-pentylcinnamaldehyde, aswell as mixtures thereof. Without being bound by theory, thecinnamaldehyde compound herein may inhibit corrosion caused by acidicmediums by undergoing an acid catalyzed polymerization reaction therebyforming a thin film on the metal surface being protected.

The corrosion inhibitor composition may optionally include analkoxylated fatty amine. Fatty amines are compounds having a long-chainalkyl group made up of hydrogen and anywhere from 6 to 26 carbon atoms,preferably 8 to 22 carbon atoms, preferably 12 to carbon atoms, morepreferably 16 to 18 carbon atoms, bonded to an amine functional group.The fatty portion of the fatty amine may be saturated or may containsites of unsaturation, for example, the fatty portion may be mono-, di-,tri-, oligo-, or poly-unsaturated. The fatty portion of the fatty aminepreferably contains sites of unsaturation from the point of view ofsolubility. The site(s) of unsaturation may be cis-double bonds,trans-double bonds, or a combination. The fatty amines may be derivablefrom fatty acids, for example by subjecting a fatty acid, either asynthetic fatty acid or a naturally occurring fatty acid, to the Nitrileprocess followed by reduction (e.g., hydrogenation), which is known bythose of ordinary skill in the art. Exemplary fatty acid startingmaterials that may be used to make the fatty amine include, for example,caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,stearic acid, arachidic acid, behenic acid, lignoceric acid, ceroticacid, myristoleic acid, palmitoleic acid, sapienic acid, oleic acid,elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, α-inolenicacid, arachidonic acid, eicosapentaenoic acid, erucic acid,docosahexaenoic acid, and the like, as well as fatty acid mixtures(natural or synthetic mixtures) such as tall oil fatty acid and itsderivatives (TOFA), coconut oil and its derivatives, tallow fatty acidand its derivatives (tallow), naphthenic acids and its derivatives, soyafatty acid and its derivatives (soya), and the like. Therefore, thefatty amines may also exist as a distribution or mixture of fatty amineswhen derived from mixtures of (naturally occurring) fatty acids.Exemplary fatty amines derivable or manufactured from fatty acids,include, but are not limited to, coco amine, stearyl amine,palmitoleylamine, oleylamine, tallow amine (e.g., Farmin TD,commercially available from Kao), tall oil fatty acid amine,laurylamine, linoleylamine, myristylamine, cetylamine, stearylamine, andsoya amine, any of which may be optionally hydrogenated, partiallyhydrogenated, or non-hydrogenated.

The fatty amine may be a fatty monoamine, such as primary fatty amines(R—NH₂), and secondary di-fatty amines (R₂—NH), or fatty lower alkyl(e.g., methyl) amines (R—NH—CH₃); or a fatty (poly)alkylene polyamine,such as fatty ethylene diamines (R—NH—(CH₂)₂—NH₂), fatty ethylenetriamines (linear or branched, R—NH—(CH₂)₂—NH—(CH₂)₂—NH₂), fattyethylene tetramines (linear or branched,R—NH—(CH₂)₂—NH—(CH₂)₂—NH—(CH₂)₂—NH₂), fatty propylene diamines(R—NH—(CH₂)₃—NH₂), fatty propylene triamines (linear or branched,R—NH—(CH₂)₃—NH—(CH₂)₃—NH₂), and fatty propylene tetramines (linear orbranched, R—NH—(CH₂)₃—NH—(CH₂)₃—NH—(CH₂)₃—NH₂). In preferredembodiments, R (above) is a mixture of long-chain alkyl groups derivedfrom naturally occurring fatty acid mixtures such as tall oil fatty acidand its derivatives (TOFA), coconut oil and its derivatives, tallowfatty acid and its derivatives (tallow), naphthenic acids and itsderivatives, soya fatty acid and its derivatives (soya), and the like.

Any of the aforementioned fatty amines may be alkoxylated to provide thealkoxylated fatty amines useful in the corrosion inhibitor compositionsof the present disclosure. Primary fatty amines may be alkoxylated withone or two polyoxyalkylene ether groups (i.e., mono- orbis-alkoxylated), and secondary fatty amines may be alkoxylated with onepolyoxyalkylene ether group (i.e., mono-alkoxylated). Suitable examplesof alkoxylated fatty amines include, but are not limited to, a coconutamine alkoxylate, a stearyl amine alkoxylate, a palmitoleylaminealkoxylate, a oleylamine alkoxylate, a tallow amine alkoxylate, a talloil amine alkoxylate, a laurylamine alkoxylate, a myristylaminealkoxylate, a cetylamine alkoxylate, a stearylamine alkoxylate, alinoleyl amine alkoxylate, a soya amine alkoxylate, as well asalkoxylated ethylene diamine variants thereof, alkoxylated trimethylenediamine variants thereof, alkoxylated diethylene triamine variantsthereof, and alkoxylated dipropylene triamine variants thereof,preferably the alkoxylated fatty amine is an ethoxylated fatty amine.

Imidazoline compounds are those compounds which can be generally formedfrom a reaction between (i) a fatty acid or an ester derivative thereof,for example a C₁ to C₁₂ alkyl ester (e.g., methyl, ethyl, etc.) of afatty acid or a glycerol ester of a fatty acid, and (ii) a polyaminewhich contains at least one ethylene diamine group (i.e., a polyaminecontaining at least one vicinal diamine). The imidazoline compound maybe a non-ionic cyclization reaction product from reaction between (i)and (ii), or the imidazoline compound may be a modified imidazoline(cationic or amphoteric). Examples of cationic imidazolines includethose non-ionic cyclization products which are further protonated byreaction with an acid or alkylated forming quaternary ammoniumfunctional groups. Examples of amphoteric imidazolines includebetaine-type imidazolines.

In some embodiments, the imidazoline compound is prepared from reactionbetween (i) tall oil fatty acid, coconut oil fatty acid, tallow fattyacid, soya fatty acid, and/or oleic acid. and (ii) any polyaminecontaining two, three, four, or more nitrogen groups, which may beprimary, secondary, or tertiary amines, so long as at least one ethylenediamine group is present that is capable of reacting with a carboxylicacid group to form an imidazoline structure. Suitable polyaninesinclude, but are not limited to, ethylene diamine, β-hydroxyethylethylene diamine, 1,2-diarminopropane, 1,2-diaminocyclohexane,2,3-dianinobutane, 2,3-diaminobutan-1-ol, propane-1,2,3-triamine,tris(2-aminoethyl)amine, tetraethylenepentamine (TEPA),diethylenetrianine (DETA), triethylentetramine (TETA),aminoethylethanolanine (AEEA), pentaethylene hexamine (PEHA), andhexaethylene heptanine (HEHA).

A wide range of molar ratios of (i) and (ii) may be employed to form theimidazoline compounds herein, however, in preferred embodiments themolar ratio of (i) to (ii) is 1:5 to 5:1, preferably 1:1 to 5:1, morepreferably 2:1 to 4:1, or any integers or non-integers in between.Imidazoline compounds that may be used in the corrosion inhibitorcompositions herein may include, but is not limited to, 1:1 (molarratio) TOFA/DETA imidazoline, 2:1 TOFAIDETA imidazoline, 1:1 TOFA/TETAimidazoline, 2:1 TOFA/TETA imidazoline, 2:1 TOFA/TETA bis-imidazoline,1:1 TOFA/TEPA imidazoline, 2:1 TOFA/TEPA imidazoline, 2:1 TOFA/TEPAbis-imidazoline, 3:1 TOFA/TEPA bis-imidazoline, 1:1 TOFA/AEEAimidazoline, 2:1 TOFA/AEEA imidazoline, 1:1 TOFA/polyamine imidazoline,2:1 TOFA/polyamine imidazoline, 2:1 TOFA/polyanine bis-imidazoline, 3:1TOFA/TEPA polyamine bis-imidazoline, 1:1 Soya/DETA imidazoline, 2:1Soya/DETA imidazoline, 1:1 Soya/TETA imidazoline, 2:1 Soya/TETAimidazoline, 2:1 Soya/TETA bis-imidazoline, 1:1 Soya/TEPA imidazoline,2:1 Soya/TEPA imidazoline, 2:1 Soya/TEPA bis-imidazoline, 3:1 TOFA/TEPAbis-imidazoline, 1:1 Soya/AEEA imidazoline, 2:1 Soya/AEEA imidazoline,1:1 Soya/polyarnine imidazoline, 2:1 Soya/polyanine imidazoline, 2:1Soya/polyaamine bis-imidazoline, 1:1 Tallow/DETA imidazoline, 2:1Tallow/DETA imidazoline, 1:1 Tallow/TETA imidazoline, 2:1 Tallow/TETAimidazoline, 2:1 Tallow/TETA bis-imidazoline, 1:1 Tallow/TEPAimidazoline, 2:1 Tallow/TEPA imidazoline, 2:1 Tallow/TEPAbis-imidazoline, 3:1 Tallow/TEPA bis-imidazoline, 1:1 Tallow/AEEAimidazoline, 2:1 Tallow/AEEA imidazoline, 1:1 Tallow/polyamineimidazoline, 2:1 Tallow/polyamine imidazoline, 2:1 Tallow/polyaminebis-imidazoline, 3:1 Tallow/TEPA polyanine bis-imidazoline, as well asmixtures thereof. Most preferably, when present, the imidazoline is 1:1TOFA-DETA imidazoline or 1:1 TOFA-AEEA.

Other secondary corrosion inhibitors which may be optionally included inthe corrosion inhibitor compositions include, but are not limited to,chromates, zinc salts, (poly)phosphates, organic phosphorus compounds(phosphonates), acetylenic alcohols (e.g., propargylic alcohol,pent-4-yn-1-ol, hexynol, ethyl octynol, octynol,3-phenyl-2-propyn-1-ol), β-unsaturated aldehydes (other thancinnamaldehydes) (e.g., crotonaldehyde), aromatic aldehydes (e.g.,furfural, p-anisaldehyde), phenones including alkenyl phenone (e.g.,(3-hydroxypropiophenone, phenyl vinyl ketone), nitrogen-containingheterocycles (e.g., piperazine, hexamethylene tetramine), quaternizedheteroarenes (e.g., 1-(benzyl)quinolinium chloride), condensationproducts of carbonyls and amines (e.g., Schiff base), and other polymersobtained from natural sources (e.g., chitin, collagen, pectin, plantgums such as gum Arabic and guar gum, etc.).

In preferred embodiments, the corrosion inhibitor composition (and thusthe acidic treatment fluid) is substantially free of secondary corrosioninhibitors. In preferred embodiments, the corrosion inhibitorcomposition (and thus the acidic treatment fluid) is substantially freeof a cinnamaldehyde compound, an alkoxylated fatty amine, and animidazoline compound.

Surfactant

The acidic treatment fluid may also optionally include one or moresurfactants. The surfactant(s), when present, may be included in anamount of 0.01 to 10%, preferably 0.1 to 8%, preferably 0.5 to 6%,preferably 1 to 4% by weight per total volume of the acidic treatmentfluid. Cationic, non-ionic, and/or amphoteric surfactants may beemployed herein.

Cationic surfactants may include, but are not limited to

-   -   a protonated amine formed from a reaction between a C₆-C₂₆ alkyl        amine compound and an acid (e.g., acetic acid, formic acid,        propionic acid, butyric acid, pentanoic acid, hexanoic acid,        oxalic acid, malonic acid, lactic acid, glyceric acid, glycolic        acid, malic acid, citric acid, benzoic acid, p-toluenesulfonic        acid, trifluoromethanesulfonic acid, hydrochloric acid, nitric        acid, phosphoric acid, sulfuric acid, hydrobromic acid,        perchloric acid, hydroiodic acid, etc.), such as protonated        salts of C₆-C₂₆ alkyl monoamines, C₆-C₂₆ alkyl (poly)alkylene        polyamines, and alkoxylated fatty amines;    -   a protonated C₆-C₂₆ alkyl amidoamine formed from a reaction        between a C₆-C₂₆ alkyl amidoamine compound and an acid (for        example the acids listed above), such as protonated forms of the        amide reaction product between any fatty acid previously listed        (or ester derivative thereof) with a polyamine (e.g.,        putrescine, cadaverine, ethylene diamine,        N¹,N¹-dinetlhylethane-1,2-diamine,        N¹,N¹-dimethylpropane-1,3-diamine,        N¹,N¹-diethylethane-1,2-diamine,        N¹,N¹-diethylpropane-1,3-diamine, spermidine,        1,1,1-tris(aminomethyl)ethane, tris(2-aminoethyl)amine,        spermine, TEPA, DETA, TETA, AEEA, PEHA, HEHA, dipropylene        triamine, tripropylene tetramine, tetrapropylene pentamine,        pentapropylene hexamine, hexapropylene heptamine, dibutylene        triamine, tributylene tetramine, tetrabutylene pentamine,        pentabutylene hexamine, hexabutylene heptamine), with specific        mention being made to protonated forms of        stearamidopropyldimethylamine, stearamidopropyldiethylamine,        stearamidoethyldiethylamine, stearamidoethyldimethylamine,        palmitamidopropyldimethylamine, palmitamidopropyldiethylamine,        palmitamidoethyldiethylamine, palmitamidoethyldimethylamine,        behenamidopropyldimethylamine, behenamidopropyldiethylmine,        behenamidoethyldiethylamine, behenamidoethyldimethylamine,        arachidamidopropyldimethylamine, arachidamidopropyldiethylamine,        arachidamidoethyldiethylamine, and        arachidamidoethyldimethylamine; and    -   a quaternary ammonium compound made from alkylation with        suitable alkylating agents (e.g., dimethyl sulfate, methyl        chloride or bromide, benzyl chloride or bromide, C₆-C₂₆ alkyl        chloride or bromide, etc.) of a tertiary C₆-C₂₆ alkyl amine, an        alkoxylated (tertiary) amine, or an aprotic nitrogenous        heteroarene (optionally substituted) having at least one        aromatic nitrogen atom with a reactive lone pair of electrons,        with specific mention being made to a C₁₀-C₁₈ alkyl trimethyl        ammonium chloride or methosulfate, a di-C₁₀-C₁₈ alkyl dimethyl        ammonium chloride or methesulfate, a C₁₀-C₁₈ alkyl benzyl        dimethyl ammonium chloride, a methyl quaternized C₆-C₂₂ alkyl        propylene diamine, a methyl quaternized C₆-C₂₂ alkyl propylene        triamine, a methyl quaternized C₆-C₂₂ alkyl propylene        tetraamine, a N—C₁₀-C₁₈ alkyl pyridinium or a quinolinium        bromide or chloride such as N-octyl pyridinium bromide, N-nonyl        pyridinium bromide, N-decyl pyridinium bromide, N-dodecyl        pyridinium bromide, N-tetradecyl pyridinium bromide, N-dodecyl        pyridinium chloride, N-cyclohexyl pyridinium bromide, naphthyl        methyl quinolinium chloride, naphthyl methyl pyridinium        chloride, and cetylpyridinium chloride, as well as mixtures        thereof.

Non-ionic surfactants may include, but are not limited to:

-   -   alkanolamides of fatty acids, that is, amide reaction products        between a fatty acid and an alkanolamine compound, such as        coconut fatty acid monoethanolamide (e.g., N-methyl coco fatty        ethanol amide), coconut fatty acid diethanolamide, oleic acid        diethanolamide, and vegetable oil fatty acid diethanolamide;    -   alkoxylated alkanolamides of fatty acids, preferably ethoxylated        and/or propoxylated variants of the alkanolamides of fatty acids        using for example anywhere from 2 to 30 EO and/or PO molar        equivalents, preferably 3 to 15 EO and/or PO molar equivalents,        preferably 4 to 10 EO and/or PO molar equivalents, preferably 5        to 8 EO and/or PO molar equivalents per moles of the        alkanolamide of the fatty acid (e.g., coconut fatty acid        monoethanolamide with 4 moles of ethylene oxide);    -   amine oxides, such as N-cocoamidopropyl dimethyl amine oxide and        dimethyl C₆-C₂₂ alkyl amine oxide (e.g., dimethyl coco amine        oxide);    -   fatty esters, such as ethoxylated and/or propoxylated fatty        acids (e.g., castor oil with 2 to 40 moles of ethylene oxide),        alkoxylated glycerides (e.g., PEG-24 glyceryl monostearate),        glycol esters and derivatives, monoglycerides, polyglyceryl        esters, esters of polyalcohols, and sorbitan/sorbitol esters;    -   ethers, such as (i) alkoxylated C₁-C₂₂ alkanols, which may        include alkoxylated C₁-C₅ alkanols, preferably ethoxylated or        propoxylated C₁-C₅ alkanols (e.g., dipropylene glycol n-butyl        ether, tripropylene glycol n-butyl ether, dipropylene glycol        methyl ether, tripropylene glycol methyl ether, diethylene        glycol n-butyl ether, triethylene glycol n-butyl ether,        diethylene glycol methyl ether, triethylene glycol methyl ether)        and alkoxylated C₆-C₂₆ alkanols (including alkoxylated fatty        alcohols), preferably alkoxylated C₇-C₂₂ alkanols, more        preferably alkoxylated C₈-C₁₄ alkanols, preferably ethoxylated        or propoxylated (e.g., cetyl stearyl alcohol with 2 to 40 moles        of ethylene oxide, lauric alcohol with 2 to 40 moles of ethylene        oxide, oleic alcohol with 2 to 40 moles of ethylene oxide,        ethoxylated lanoline derivatives, laureth-3, ceteareth-6,        ceteareth-11, ceteareth-15, ceteareth-16, ceteareth-17,        ceteareth-18, ceteareth-20, ceteareth-23, ceteareth-25,        ceteareth-27, ceteareth-28, ceteareth-30, isoceteth-20,        laureth-9/myreth-9, and PPG-3 caprylyl ether); (ii) alkoxylated        polysiloxanes; (iii) ethylene oxide/propylene oxide copolymers        (e.g., PPG-1-PEG-9-lauryl glycol ether, PPG-12-buteth-16,        PPG-3-buteth-5, PPG-5-buteth-7, PPG-7-buteth-10,        PPG-9-buteth-12, PPG-12-buteth-16, PPG-15-buteth-20,        PPG-20-buteth-30, PPG-28-buteth-35, and PPG-33-buteth-45);        and (iv) alkoxylated alkylphenols.

Amphoteric surfactants may also be incorporated into the corrosioninhibitor compositions, and may include betaine-type compounds such as:

-   -   C₆-C₂₂ alkyl dialkyl betaines, such as fatty dimethyl betaines        (R—N(CH₃)₂ ⁽⁺⁾—CH₂COO⁻), obtained from a C₆-C₂₂ alkyl dimethyl        amine which is reacted with a monohaloacetate salt (e.g., sodium        monochloroacetate), such as C₁₂-C₁₄ dimethyl betaine        (carboxylate methyl C₁₂-C₁₄ alkyl dimethylammonium);    -   C₆-C₂₂ alkyl amido betaines (R—CO—NH—CH₂CH₂CH₂—N(CH₃)₂        ⁽⁺⁾—CH₂COO⁻ or R—CO—NH—CH₂CH₂—N(CH₃)₂ ⁽⁺⁾—CH₂COO⁻), obtained by        the reaction of a monohaloacetate salt (e.g., sodium        monochloroacetate) with the reaction product of either dimethyl        amino propylamine or dimethyl amino ethylamine with a suitable        carboxylic acid or ester derivatives thereof, such as C₁₀-C₁₈        amidopropyl dimethylamino betaine;    -   C₆-C₂₂ alkyl sultaines or C₆-C₂₂ alkyl amido sultaines, which        are similar to those C₆-C₂₂ alkyl dialkyl betaines or C₆-C₂₂        alkyl amido betaines described above except in which the        carboxylic group has been substituted by a sulfonic group        (R—N(CH₃)₂ ⁽⁺⁾—CH₂CH₂CH₂SO₃ ⁻ or R—CO—NH—CH₂CH₂CH₂—N(CH₃)₂        ⁽⁺⁾—CH₂CH₂CH₂SO₃ ⁻ or R—CO—NH—CH₂CH₂—N(CH₃)₂ ⁽⁺⁾—CH₂CH₂CH₂SO₃ ⁻)        or a hydroxysulfonic group (R—N(CH₃)₂(⁺)—CH₂CH(OH)—CH₂SO₃ ⁻ or        R—CO—NH—CH₂CH₂CH₂—N(CH₃)₂(⁺)—CH₂CH(OH)—CH₂SO₃ ⁻ or        R—CO—NH—CH₂CH₂—N(CH₃)₂(⁺)—CH₂CH(OH)—CH₂SO₃ ⁻), such as C₁₀-C₁₈        dimethyl hydroxysultaine and C₁₀-C₁₈ amido propyl dimethylamino        hydroxysultaine.

Organic Solvent

The base solvent of the acidic treatment fluid is preferably water.However, the acidic treatment fluid may also optionally include one ormore organic solvents, which may aid solvation of the variousingredients as well as facilitate transfer of the active ingredients tothe appropriate location within the wellbore or geological formation. Inpreferred embodiments, organic solvent(s) may be added in amounts of 1to 50%, preferably 2 to 40%, preferably 3 to 30%, preferably 5 to 20%,preferably 10 to 18%, preferably 15 to 16% by weight per total volume ofthe acidic treatment fluid. The organic solvent may be at least oneselected from the group consisting of a polar aprotic solvent, anaromatic solvent, a terpineol, a mono alcohol with 1 to 12 carbon atoms,and a polyol with 2 to 18 carbon atoms. Acceptable organic solventsinclude, but are not limited to, formamide, dimethyl formamide, dimethylacetamide, methanol, ethanol, propanol, isopropanol, n-butanol,isobutanol, n-pentanol, n-hexanol, terpineol, menthol, prenol,3-methyl-3-buten-1-ol, 2-ethyl-1-hexanol, 2-ethyl-1-butanol,2-propylheptan-1-ol, 2-butyl-1-octanol, ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, ethylene glycol methylether, ethylene glycol ethyl ether, ethylene glycol propyl ether,ethylene glycol butyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, propylene glycol, dipropylene glycol,propylene glycol monomethyl ether, pyrocatechol (1,2-benzenediol),resorcinol (1,3-benzenediol), phenol, cresol, benzyl alcohol,1,3-propanediol, 1,3-butanediol, 2-butoxyethanol, 1,4-butanediol,1,6-hexanediol, glycerol, pentaerythritol, manitol, sorbitol, as well asmixtures thereof.

Additives

The acidic treatment fluids may optionally further include one or moreadditives to modify the properties or functions of the acidic treatmentfluid, as needed. Typically, when present, the additive(s) may beincorporated in an amount of less than 10%, preferably less than 8%,preferably less than 6%, preferably less than 4%, preferably less than2%, preferably less than 1%, preferably less than 0.5%, preferably lessthan 0.1% by weight per total volume of the acidic treatment fluid.

Additive(s) suitable for use in oil and gas well operations are known bythose of ordinary skill in the art, and may include, but are not limitedto,

-   -   viscosity modifying agents e.g., bauxite, bentonite, dolomite,        limestone, calcite, vaterite, aragonite, magnesite, taconite,        gypsum, quartz, marble, hematite, limonite, magnetite, andesite,        garnet, basalt, dacite, nesosilicates or orthosilicates,        sorosilicates, cyclosilicates, inosilicates, phyllosilicates,        tectosilicates, kaolins, montmorillonite, fullers earth,        halloysite, polysaccharide gelling agents (e.g., xanthan gum,        scleroglucan, and diutan) as well as synthetic polymer gelling        agents (e.g., polyacrylamides and co-polymers thereof, see U.S.        Pat. No. 7,621,334—incorporated herein by reference in its        entirety), psyllium husk powder, hydroxyethyl cellulose,        carboxymethylcellulose, and polyanionic cellulose, poly(diallyl        amine), diallyl ketone, diallyl amine, styryl sulfonate, vinyl        lactam, laponite;    -   chelating agents e.g., ethylene dianine tetraacetic acid (EDTA),        diethylene tnamine pentaacetic acid (DPTA), hydroxyethylene        dianine triacetic acid (HEDTA), ethylene diamine        di-ortho-hydroxy-phenyl acetic acid (EDDHA), ethylene diamine        di-ortho-hydroxy-para-methyl phenyl acetic acid (EDDHMA),        ethylene diamine di-ortho-hydroxy-para-carboxy-phenyl acetic        acid (EDDCHA);    -   stabilizing agents e.g., polypropylene glycol, polyethylene        glycol, carboxymethyl cellulose, hydroxyethyl cellulose,        polysiloxane polyalkyl polyether copolymers, acrylic copolymers,        alkali metal alginates and other water soluble alginates,        carboxyvinyl polymers, polyvinylpyrollidones, polyacrylates;    -   dispersing agents e.g., polymeric or co-polymeric compounds of        polyacrylic acid, polyacrylic acid/maleic acid copolymers,        styrene/maleic anhydride copolymers, polymethacrylic acid and        polyaspartic acid;    -   scale inhibitors e.g., sodium hexametaphosphate, sodium        tripolyphosphate, hydroxyethylidene diphosphonic acid,        aminotris(methylenephosphonic acid (ATMP), vinyl sulfonic acid,        allyl sulfonic acid, polycarboxylic acid polymers such as        polymers containing 3-allyloxy-2-hydroxy-propionic acid        monomers, sulfonated polymers such as vinyl monomers having a        sulfonic acid group, polyacrylates and co-polymers thereof;    -   defoaming agents e.g., silicone oils, silicone oil emulsions,        organic defoamers, emulsions of organic defoamers,        silicone-organic emulsions, silicone-glycol compounds,        silicone/silica adducts, emulsions of silicone/silica adducts;    -   emulsifiers such as a tallow amine, a ditallow amine, or        combinations thereof, for example a 50% concentration of a        mixture of tallow alkyl amine acetates, C16-C₁₈ (CAS 61790-60)        and ditallow alkyl amine acetates (CAS 71011-03-5) in a suitable        solvent such as heavy aromatic naphtha and ethylene glycol;    -   as well as mixtures thereof.

In some embodiments, the acidic treatment fluid is substantially free ofa surfactant. In some embodiments, the acidic treatment fluid issubstantially free of an organic solvent. In some embodiments, theacidic treatment fluid is substantially free of an additive (e.g.,viscosity modifying agents, chelating agents, stabilizing agents,dispersing agents, scale inhibitors, and/or defoaming agents). Inpreferred embodiments, the acidic treatment fluid is substantially freeof a polysaccharide (e.g., xanthan gum, scleroglucan, and diutan), asynthetic polymer (e.g., polyacrylamides and co-polymers thereof), and aquaternary ammonium surfactant.

Oil and Gas Well

The corrosion inhibitor compositions of the present disclosure may bedeployed during any upstream (exploration, field development, andproduction operations), midstream (transportation e.g., by pipeline,processing, storage, and distribution), or downstream (manufacturing,refining, wholesale) oil and gas process where metal corrosion is aconcern. However, the corrosion inhibitor compositions are particularlyeffective at combating corrosion caused by concentrated acidic fluids,and thus are advantageously employed during upstream processes, morepreferably during acid stimulation treatments where corrosion caused byhighly acidic mediums is a primary concern, even more preferably duringmatrix acidizing treatments.

In some embodiments, the acidic treatment fluids may be injected downthe annulus of a well and optionally flushed with solvent. In someembodiments, the acidic treatment fluid is pre-formed above well bycombining the acid (aq.) and the corrosion inhibitor composition, andany optional components, followed by injecting the pre-formed acidictreatment fluid downhole for the acid stimulation operation. In someembodiments, the acid (aq.) and the corrosion inhibitor composition (andany optional components) are injected downhole as separate streams,combining downhole to form the acidic treatment fluid for acidstimulation. The corrosion inhibitor compositions may be injectedbefore, after, or simultaneously with the acid (aq.) for use in thestimulation process. Injection may proceed through suitable injectionlines to areas where acid stimulation treatment is desired or wherecorrosion can, or is likely to, occur through capillaries or umbilicallines (in many cases at the wellhead if suitable metallurgy is useddownhole). Injection may be performed manually or it may be automatic,for example, by using chemical injection pumps. In some embodiments, theacidic treatment fluid may be stored in a chemical storage tank and achemical injection pump associated therewith may be used to introducethe acidic treatment fluid into the desired location of the operation.In any of the above applications, the acidic treatment fluid or any ofits components combinable downhole may be injected continuously and/orin batches. The chemical injection pump(s) can be automatically ormanually controlled to inject any amount of the acidic treatment fluidneeded for acidizing operations or any amount of the corrosion inhibitorcomposition suitable for inhibiting corrosion.

The acidic treatment fluids may be in contact with many different typesof surfaces on tubing and field equipment that are susceptible tocorrosion. Illustrative examples of which include, but are not limitedto, separation vessels, dehydration units, gas lines, pipelines, coolingwater systems, valves, spools, fittings (e.g., such as those that makeup the well Christmas tree), treating tanks, storage tanks, coils ofheat exchangers, fractionating columns, cracking units, pump parts(e.g., parts of beam pumps), and in particular downhole surfaces thatare most likely to come into contact with the acidic treatment fluidsduring stimulation operations, such as those casings, liners, pipes,bars, pump parts such as sucker rods, electrical submersible pumps,screens, valves, fittings, and the like.

Any metal surface that may come into contact with the acidic treatmentfluid may be protected by the corrosion inhibitor compositions of thepresent disclosure. Typical metals found in oil and gas fieldenvironments that may be protected include carbon steels (e.g., mildsteels, high-tensile steels, higher-carbon steels), including AmericanPetroleum Institute (API) carbon steels; high alloy steels includingchrome steels, ferritic alloy steels, austenitic stainless steels,precipitation-hardened stainless steels high nickel content steels;galvanized steel, aluminum, aluminum alloys, copper, copper nickelalloys, copper zinc alloys, brass, ferritic alloy steels, and anycombination thereof. Specific examples of typical oil field tubularsteels include X60, J-55, N-80, L-80, P:105, P110, and high alloy chromesteels such as Cr-9, Cr-13, Cr-2205, Cr-2250, and the like. In preferredembodiments, the methods herein inhibit corrosion of API X60 carbonsteel.

The corrosion inhibitor compositions disclosed herein performsurprisingly well to inhibit corrosion in highly acidic mediums (such asin the acidic treatment fluids) at temperatures even up to 180° C., forexample at temperatures of 25 to 180° C., preferably 30 to 160° C.,preferably 40 to 140° C., preferably 45 to 120° C.

Corrosion rate is the speed at which metals undergo deterioration withina particular environment. The rate may depend on environmentalconditions and the condition or type of metal. Factors often used tocalculate or determine corrosion rate include, but are not limited to,weight loss (reduction in weight of the metal during reference time),area (initial surface area of the metal), time (length of exposure time)and density of the metal. Corrosion rate may be measured according tothe American Society for Testing and Materials (ASTM) standard weightloss (immersion) test (e.g., according to ASTM G31-72 and described inthe Examples), and may be computed using millimeters per year (mm/y) ormils penetration per year (mpy). In some embodiments, the methodprovides a corrosion rate of 0.1 to 1.5 mm/y, preferably 0.2 to 1.2mm/y, preferably 0.3 to 1.0 mm/y, preferably 0.35 to 0.95 mm/y,preferably 0.4 to 0.9 mm/y, preferably 0.45 to 0.85 mm/y, preferably 0.5to 0.8 mm/y, preferably 0.55 to 0.75 mm/y. In some embodiments, themethod provides a corrosion rate of to 50 mpy, preferably 10 to 45 mpy,preferably 12 to 40 mpy, preferably 15 to 38 mpy, preferably 17 to 36mpy, preferably 20 to 34 mpy, preferably 24 to 32 mpy, preferably 26 to31 mpy.

Corrosion inhibition efficiencies (IE %) may be measured by comparingthe corrosion rates obtained from acidic treatment fluids with andwithout corrosion inhibitors using weight loss (immersion) studies,electrochemical impedance spectroscopy (EIS), linear polarizationresistance (LPR), potentiodynamic polarization (PDP), or other similarmethods. In some embodiments, the method described herein achieves acorrosion inhibition efficiency of 45 to 92%, preferably 50 to 90%,preferably 52 to 89%, preferably 55 to 88%, preferably 58 to 85%,preferably 59 to 80%, preferably 60 to 75%.

Of course, the methods herein do not preclude introduction of otherknown chemical treatments into oil and gas field production anddownstream transportation, distribution, and/or refining systems, andthus the acidic treatment fluids may be used in conjunction with otherchemical treatments known to those of ordinary skill in the art,including, but not limited to, hydrate inhibitors, scale inhibitors,asphaltene inhibitors, paraffin inhibitors, H₂S scavengers, O₂scavengers, emulsion breakers, foamers and de-foamers, and waterclarifiers.

The examples below are intended to further illustrate protocols forpreparing and testing the acidic treatment fluids and are not intendedto limit the scope of the claims.

Where a numerical limit or range is stated herein, the endpoints areincluded. Also, all values and subranges within a numerical limit orrange are specifically included as if explicitly written out.

As used herein the words “a” and “an” and the like carry the meaning of“one or more.”

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

All patents and other references mentioned above are incorporated infull herein by this reference, the same as if set forth at length.

Examples Experimental Procedure Materials and Chemicals

Purified gelatin was obtained from Sigma Aldrich (Product Number 48723,CAS 9000-70-8), the molecular weight of gelatin cannot be determinedaccurately due to the complexity of gelatin molecular structure; theconcentration was expressed in terms of % weight by volume. HCl (SigmaAldrich), Potassium Iodide (Sigma Aldrich) and API X60 carbon steel froma typical oil pipeline was taken as test specimens.

Preparation of Carbon Steel Specimens

Chemical compositions of the specimen utilized are illustrated inTable 1. The carbon steel specimen was mechanically cut into couponswith dimensions (3 cm×3 cm×1 cm) for weight loss measurements andcylindrical with a total surface area of 3.14 cm² for electrochemicalmeasurements. Prior to the experiments the carbon steel coupons were wetpolished with 120, 240, 320, 400, 600, and 800 grit silicon carbidepaper, thoroughly rinsed with double distilled water to give amirror-like surface. After polishing, the specimens were degreased withacetone in an ultrasonic bath for 10 min, dried and enclosed in sealedwater-proof bags and stored in a moisture-free desiccator prior to use.

Preparation of Inhibitor Solutions

Analytical grade HCl (Sigma Aldrich) was diluted to 15% HCl solutionusing double distilled water. Five different concentrations (0.5%, 1.0%,1.5%, 2.0% and 2.5%) of the gelatin inhibitor were separately preparedin 15% HCl solutions and used for the experiments.

Weight Loss Measurement

The weight loss (Immersion Test) measurement was carried out accordingto the American Society for Testing and Materials (ASTM) standardmethod. Pre-weighed carbon steel coupons were immersed in the acidssolutions without and with the different concentrations of the gelatininhibitor for 24 h interval maintained at room temperature. Aftercompletion the coupons were retrieved, washed in 1M HCl for 10s,thoroughly washed with water, dried after rinsing in acetone and weighedto determine the weight loss. The experiments were carried out induplicate but only the mean value of the weight losses (g) are reportedand used for computation of the corrosion rate. The corrosion rates werecalculated in mm/y and mpy using Eqs (1) and (2) respectively.

$\begin{matrix}{{{Corrosion}{rate}\left( {{mm}/{year}} \right)} = \frac{W \times {8.7}6 \times 10^{4}}{A \times T \times D}} & (1)\end{matrix}$ $\begin{matrix}{{{Corrosion}{rate}({mpy})} = \frac{W \times 3.45 \times 10^{6}}{A \times T \times D}} & (2)\end{matrix}$

where, W represents the mass loss in g, A is the surface area exposed incm², T is the time of exposure in hours, and D is the density in g/cm³(7.86 g/cm³ for mild steel).

TABLE 1 Chemical composition of the X60 carbon steel specimen used inthe study. Element Fe Cr C Si Mn Cu Ni Mo Al Nb V Composition <96.20.121 0.125 0.52 1.830 0.296 0.091 0.079 0.043 0.053 0.078 (wt %)

The inhibition efficiency was calculated using the Eq. 3. The corrosioninhibitor efficiency is a measurement of the effectiveness of thecorrosion inhibitor, and the value ranges between 0 and 100%.

$\begin{matrix}{{\%{IE}} = {\frac{{CR_{o}} - {CR_{i}}}{CR_{o}} \times 100}} & (3)\end{matrix}$

where, CR₀ is the corrosion rate of carbon steel in the absence of aninhibitor and CR_(i) is the corrosion rate of carbon steel in thepresence of inhibitor.

Electrochemical Measurements

The electrochemical measurements were performed by using three cellelectrodes, connected to Gamry Potentiostat/Galvanostat (Model G-3000)instrument. The conventional three-electrode set up composed of asilver/silver chloride electrode (Ag/AgCl) as the reference electrode,graphite as the counter electrode and one of the different steelspecimens as the working electrode. Three electrochemical techniques,namely potentiodynamic polarization (PDP), linear polarizationresistance (LPR), and electrochemical impedance spectroscopy (EIS) wereused to study the corrosion behavior of carbon steel in the absence andpresence of different concentrations of gelatin in 15% HCl at 25° C.

Prior to each electrochemical measurement, the working electrode wasimmersed in the test solution for 1 h to attain steady state conditionof open circuit potential (OCP). The EIS was conducted at a frequency of100 kHz to 10 mHz and an amplitude of 10 mV after the 3600 s opencircuit potential. The voltage ranged from −0.25V to +0.25V vs. E_(OC)at a scan rate of 0.2 mV/s was used for PDP measurements. LPRmeasurements were taken at E_(corr)±10 mV at a scan rate of 0.25 mV/s.Gamry EChem Analyst 5.5 software was used to do the electrochemical dataanalysis and curve fittings.

Characterization Techniques SEM/EDX

The surface morphology of both inhibited and uninhibited specimens werestudied using SEM with EDX to determine the elemental composition of thesteel surface and the corrosion products in the inhibited anduninhibited specimens. The SEM/EDX characterizations were carried out oncoupons immersed in 2.5% gelatin solution with and without added KI inthe 15% HCl.

ATR-FTIR

The FTIR analysis of the pure gelatin and the corrosion product wasperformed using Shimadzu FTIR-8400S spectrophotometer. Analysis of thesamples was performed scanning through 400-4000 cm-1 wave number range.ATR-FTIR was carried out on pure gelatin sample and carbon steelsurfaces after 24 hours immersion in 15% HCl solution in the presence of2.5% gelatin without and with the addition of 0.05% KI.

UV-Visible Spectroscopy

UV-Visible analysis was carried out using Jasco V-770 spectrophotometerin a range of 200-800 nm. The UV-Visible spectra were collected forsolutions of the 2.5% gelatin in 15% HCl recorded prior to immersion ofthe carbon steel, and solutions of 2.5% gelatin in the 15% HCl and 2.5%gelatin+0.05% KI in the 15% HCl after 24 hours immersion of the carbonsteel. The spectral profiles were then compared to predict whether acomplex is formed with the metal surface.

Results and Discussion Weight Loss Measurements

The corrosion parameters obtained by conducting weight loss measurementsfor the carbon steel in the absence and presence of differentconcentration of gelatine in 15% HCl at room temperature are tabulatedin Table 2. The corrosion rate values decreased with the increase in theconcentration of gelatin. It is apparent that the inhibition efficiencyincreased with the increase in inhibitor concentration. This behaviorcould be explained based on the strong interaction of the inhibitormolecules with the metal surface resulting in adsorption of theinhibitor molecules of the metal surface. The extent of adsorptionincreases with the increase in concentration of the inhibitor leading toincreased inhibition efficiency. The maximum inhibition efficiency(70.42%) was observed for inhibitor concentration of 2.5% w/v. Inhibitormolecules generally suppress dissolution of the metal by formingprotective film adsorbed on the metal surface, this blocks the corrosivespecies from reaching the metal surface. Hence, gelatin could providegood corrosion protection at 25° C. in 15% HCl acid up to the testduration of 24 h and shows high corrosion-inhibitor efficiency. FIGS. 2and 3 show images of the coupons immersed in 200 ml of the differentgelatin concentrations just after immersion and after 24 hours ofimmersion. It is worth noting that no visible pitting or localizedcorrosion was observed on any of the coupons after the tests usinggelatin.

Synergistic Effect of Addition of KI

The addition of potassium iodide (KI) additive increases the corrosionefficiency of the gelatin inhibitor due to synergism. The effect KI andother additives claimed to be of beneficial action on corrosioninhibitors in acidizing environments has been investigated. See M.Finsgar, J. Jackson, Application of corrosion inhibitors for steels inacidic media for the oil and gas industry: A review, Corros. Sci. 86(2014) 17-41—incorporated herein by reference in its entirety. Theaddition of KI in acidic media have been reported synergisticallyincrease the corrosion inhibition efficiency of organic inhibitors. SeeA. Y. Musa, A. B. Mohamad, A. A. H. Kadhum, M. S. Takriff, L. T. Tien,Synergistic effect of potassium iodide with phthalazone on the corrosioninhibition of mild steel in 1.0 M HCl, Corros. Sci. 53 (2011) 3672-3677;K. Aramaki, N. Hackerman, Inhibition Mechanism of Medium-SizedPolymethyleneimine, J. Electrochem. Soc. Electrochem. Sci. 116 (1969)568-574; and A. E.-A. S. Fouda, A. M. El-Azaly, Synergistic Effect ofPotassium Iodide with Some Heterocyclic Compounds on the CorrosionInhibition of 304 Stainless Steel in Hydrochloric Acid Solution, J.Bio-Tribo-Corrosion. 3 (2017) 1-10-each incorporated herein by referencein their entirety. The halide ions improve adsorption of the inhibitorcations via the formation of intermediate bridges between the positivelycharged metal surface and the positive end of the inhibitor molecule.The synergistic effect between the halide ions and the inhibitormolecules is said to results from an increased surface coverage whicharise from the cation-anion pair interaction initiated by the specificadsorption of the halide ions onto the metal surface. See E. E. Oguzie,Y. Li, F. H. Wang, Corrosion inhibition and adsorption behavior ofmethionine on mild steel in sulfuric acid and synergistic effect ofiodide ion, J. Colloid Interface Sci. 310 (2007) 90-98—incorporatedherein by reference in its entirety. Synergism between corrosioninhibitors and KI has been expressed in terms of a synergism parameter(S) according to equation 4. See K. Aramaki, N. Hackerman, InhibitionMechanism of Medium-Sized Polymethyleneimine, J. Electrochem. Soc.Electrochem. Sci. 116 (1969) 568-574; I. O. Arukalam, Durability andsynergistic effects of KI on the acid corrosion inhibition of mild steelby hydroxypropyl methylcellulose, Carbohydr. Polym. 112 (2014)291-299—each incorporated herein by reference in their entirety. If Sapproaches unity implies there are no interactions between KI and theinhibitor molecules, while S>1 implies a synergistic effect, that isthere exist a cooperative co-adsorption and S<1 implies an antagonisticinteraction, that is there exist a competitive co-adsorption between theinhibitor molecules and KI.

$\begin{matrix}{S = \frac{1 - \left\lbrack {\left( {\theta_{1} + \theta_{2}} \right) - \left( {\theta_{1}\theta_{2}} \right)} \right\rbrack}{1 - \theta_{1 + 2}^{t}}} & (4)\end{matrix}$

where θ₁ is the surface coverage of (KI), θ₂ is the surface coverage ofgelatin and θ₁₊₂′ is the surface coverage of gelatin and KI mixture. SeeM. M. Solomon, H. Gerengi, T. Kaya, E. Kaya, S. A. Umoren, Synergisticinhibition of St37 steel corrosion in 15% H₂SO₄ solution by chitosan andiodide ion additives, Cellulose. 24 (2017) 931-950—incorporated hereinby reference in its entirety. Surface coverage 0=(IE %/100). See M. M.Solomon, S. A. Umoren, Enhanced corrosion inhibition effect ofpolypropylene glycol in the presence of iodide ions at mildsteel/sulphuric acid interface, J. Environ. Chem. Eng. 3 (2015)1812-1826—incorporated herein by reference in its entirety.

The calculated synergism parameters are given in Table 2, as can be seenall values of S were less than unity implying an antagonisticinteraction between the gelatin inhibitor and KI. The gelatin moleculesand the KI species can be said to be competitively co-adsorbed on themetal surface. It was also observed that corrosion inhibition efficiencyof the lowest gelatin concentration (0.5% w/v) increases from 55.87% to78.87% and that of the highest gelatin concentration (2.5% w/v)increases from 70.42% to 84.51% on addition of very low concentration ofiodide ions (Table 2).

TABLE 2 Weight loss results for X60 carbon steel in 15% HCl in theabsence and presence of different concentrations of gelatin and with theaddition of 0.05 w/v % KI at 25° C. Concn of gelatin Weight lossCorrosion rate Efficiency S ( w/v %) (g) mpy mm/y IE (%) — Blank 0.137383.70 2.13 — — 0.5 0.0606 36.94 0.94 55.87 — 1.0 0.0551 33.59 0.85 60.09— 1.5 0.0507 30.91 0.78 63.38 — 2.0 0.0458 27.92 0.71 66.67 — 2.5 0.040924.93 0.63 70.42 — 0.05 KI 0.0406 24.75 0.63 70.42 — 0.5 + KI 0.028817.56 0.45 78.87 0.62 2.5 + KI 0.0213 12.99 0.33 84.51 0.56

Electrochemical Measurements Electrochemical Impedance Spectroscopy(EIS)

The inhibition performance of gelatine for carbon steel corrosion in 15%HCl solution was further investigated using EIS measurements. TheNyquist and Bode plots for the carbon steel (CS) in 15% HCl without andwith various concentrations of gelatin are presented in FIGS. 4A and 4Brespectively. The Nyquist plots are characterized by one capacitivesemi-circular arc which corresponds to one time-constant in the Bodeplots over the entire range of frequency. This shows that the corrosionmechanism is mainly controlled by charge transfer processes. See L. Guo,G. Ye, I. B. Obot, X. Li, X. Shen, W. Shi, X. Zheng, Synergistic Effectof Potassium Iodide with L-Tryptophane on the Corrosion Inhibition ofMild Steel: A Combined Electrochemical and Theoretical Study, Int. J.Electrochem. Sci. 12 (2017) 166-177—incorporated herein by reference inits entirety. The imperfect semi-circular nature of the capacitive arcscould be ascribed to surface inhomogeneities and roughness of coupons.The diameters of the Nyquist plots in the presence of various inhibitorconcentrations were larger than that without inhibitor (blank). Thisimplies that the inhibitor forms protective film on the surface of themetal thereby increasing the impedance of the metal surface toelectrochemical corrosion. And this diameter increases with increasingthe inhibitor concentration, an indication that the inhibitionefficiency is in direct proportionality to the concentration. See P.Lowmunkhong, D. Ungthararak, P. Sutthivaiyakit, Tryptamine as acorrosion inhibitor of mild steel in hydrochloric acid solution, Corros.Sci. 52 (2010) 30-36; Y. Tang, X. Yang, W. Yang, Y. Chen, R. Wan,Experimental and molecular dynamics studies on corrosion inhibition ofmild steel by 2-amino-5-phenyl-1,3,4-thiadiazole, Corros. Sci. 52 (2010)242-249; and M. Prabakaran, S. H. Kim, V. Hemapriya, I. M. Chung, Tragiaplukenetii extract as an eco-friendly inhibitor for mild steel corrosionin HCl 1 M acidic medium, Res. Chem. Intermed. 42 (2016) 3703-3719—eachincorporated herein by reference in their entirety. The inhibitor formedthe protective adsorbed layer on the metal surface by formingcoordination bond between N atoms in the inhibitor and the metalsurface. Increasing the concentration of the inhibitor increases therate of interaction between the N-atoms in the gelatine and the metal atthe active sites leading to more adsorption of the gelatin molecules onthe metal surface. See K. Al Mamaril, H. Elmsellem, N. K. Sebbar, A.Elyoussfi, H. Steli, M. Ellouz, Y. Ouzidan, A. Nadeem, E. M. Essassi, F.El-Hajjaji, Electrochemical and theoretical quantum approaches on theinhibition of mild steel corrosion in HCl using synthesizedbenzothiazine compound J. Mater. Environ. Sci. 7 (2016)3286-3299—incorporated herein by reference in its entirety. Theinhibitor molecules suppress the dissolution of the carbon steel byforming inhibitor/metal complex. This complex adsorbed to the surfaceand effectively blocks it from the corrosive media. See S. Paramasivam,K. Kulanthai, G. Sadhasivam, R. Subramani, Corrosion Inhibition of MildSteel in Hydrochloric Acidusing4-(pyridin-2yl)-Np-tolylpiperazine-1-carboxamide, Int. J.Electrochem. Sci. 11 (2016) 3393-3414—incorporated herein by referencein their entirety. The Bode impedance modulus plots show linear portionsat intermediate frequencies. And this linearity at intermediatefrequencies is more pronounced in the presence of the gelatine inhibitorsignifying higher slopes than the blank solution. See S. Kumar, H.Vashisht, L. O. Olasunkanmi, I. Bahadur, H. Verma, G. Singh, I. B. Obot,E. E. Ebenso, Experimental and theoretical studies on inhibition of mildsteel corrosion by some synthesized polyurethane tri-block co-polymers,Sci. Rep. 6 (2016) 1-18—incorporated herein by reference in itsentirety. The linearity increases with increasing the gelatinconcentration, indicating higher inhibition efficiency with increasinggelatin concentration. The equivalent circuit employed to fit the EISspectra is shown in FIG. 4C. The accuracy of the fit was between0.16×10⁻⁴ and 1.5×10⁻⁴ in all plots. The model utilized to fit thespectra includes R_(s) (solution resistance between working and counterelectrodes), CPE_(f) (constant phase angle element of film), R_(f) (filmresistance), and CPE_(dl) (double layer constant phase element) andR_(ct) (charge transfer resistance). The calculated electrochemicalparameters obtained from the fitting are presented in Table 3. Thepercentage inhibition efficiencies (% IE) were evaluated from equation5:

$\begin{matrix}{{{{IE}({EIS})}\%} = {\left( {1 - \frac{R_{P}}{R_{PI}}} \right) \times 100}} & (5)\end{matrix}$

where R_(p) (sum of R_(ct) and R_(f)) and R_(PI) represent polarizationresistances absence and presence of gelatin respectively.

Rather than behaving as a pure capacitor, the double layer formed by theadsorption of gelatin molecules on the metal surface behaves as constantphase element (CPE). To give a more accurate fit, constant phase element(CPE) was substituted for the capacitance element. See C. Verma, M. A.Quraishi, E. E. Ebenso, I. B. Obot, A. El Assyry, 3-Amino alkylatedindoles as corrosion inhibitors for mild steel in 1M HCl: Experimentaland theoretical studies, J. Mol. Liq. 219 (2016) 647-660; and A.Y.Adesina, Z. M. Gasem, A. Madhan Kumar, Corrosion Resistance Behavior ofSingle-Layer Cathodic Arc PVD Nitride-Base Coatings in 1M HCl and 3.5pct NaCl Solutions, Metall. Mater. Trans. B Process Metall. Mater.Process. Sci. 48 (2017) 1321-1332—each incorporated herein by referencein their entirety. The impedance of the CPE is evaluated from equation6:

Z _(CPE) =Y _(o) ⁻¹(jω)^(−n)  (6)

where Y_(o) is the magnitude of CPE, j is the square root of −1, o isangular frequency and n is phase shift. See M. Larif, A. Elmidaoui, A.Zarrouk, H. Zarrok, R. Salghi, B. Hammouti, H. Oudda, F. Bentiss, Aninvestigation of carbon steel corrosion inhibition in hydrochloric acidmedium by an environmentally friendly green inhibitor, Res. Chem.Intermed. 39 (2013) 2663-2677—incorporated herein by reference in itsentirety.

TABLE 3 Impedance parameters for X60 carbon steel in 15% HCl in theabsence and presence of different concentrations of gelatin at 25° C.CPE_(f) CPE_(dl) Gelatin R₅ Y_(ol) R_(f) Cdl_(f) Y_(o2) R_(ct) R_(p)C_(dl) Conc. (Ω (μΩs^(n) (Ω (μF (μΩs^(n) (Ω (Ω (μF χ² × IE (w/v %) cm²)cm⁻²) n₁ cm²) cm⁻²) cm⁻²) n₂ cm²) cm²) cm⁻²) 10⁻³ (%) Blank 0.80 212.700.96 1.40 172.11 1591.0 0.60 20.65 22.05 191.48 1.455 — 0.5 0.77 19.311.11 0.83 30.43 653.7 0.70 53.69 54.52 189.16 1.192 59.56 1.5 0.58 56.411.00 2.62 56.41 591.1 0.63 76.75 79.37 99.10 1.100 72.22 2.5 0.86 150.300.73 24.95 38.40 2.3 1.00 159.90 184.85 2.30 0.647 88.07

The double layer capacitances C_(dl) were evaluated from equation 7:

C _(dl) =Y _(o)(ω_(max))^(n−1)  (7)

where ω_(max)=2πf_(max); f_(max) is the frequency at which imaginarycomponent of the impedance spectrum is maximum. See J. Chen, Y. Qiang,S. Peng, Z. Gong, S. Zhang, L. Gao, B. Tan, S. Chen, L. Guo,Experimental and computational investigations of2-amino-6-bromobenzothiazole as a corrosion inhibitor for copper insulfuric acid, J. Adhes. Sci. Technol. (2018) 1-16; and M. Mobin, S.Zehra, R. Aslam, L-Phenylalanine methyl ester hydrochloride as a greencorrosion inhibitor for mild steel in hydrochloric acid solution and theeffect of surfactant additive, RSC Adv. 6 (2016) 5890-5902—eachincorporated herein by reference in their entirety.

A significant increase in the charge transfer resistance (Ret) wasobserved in the presence of the inhibitor (Table 3). The Ret, increaseswith increasing the concentration of the gelatin leading to the enhancedinhibitor efficiency. This behaviour is due to the formation of surfacefilm on the metal surface by the inhibitor molecules. The surface filmprotects the carbon steel by isolating it from the corroding mediathereby impeding further charge and mass transfer. As can be seen fromTable 3, the Y_(o2) and C_(dl) values decreases with the increasingconcentration of gelatin. This decrease in the concentration of C_(dl)results from the decrease in local dielectric constant and/or anincrease in the thickness of the electrical double layer, suggestingthat gelatin molecule functions by adsorption at the metal/solutioninterface. See P. Roy, P. Karfa, U. Adhikari, D. Sukul, Corrosioninhibition of mild steel in acidic medium by polyacrylamide grafted Guargum with various grafting percentage: Effect of intramolecularsynergism, Corros. Sci. 88 (2014) 246-253; C. B. Verma, M. A. Quraishi,A. Singh, 2-Aminobenzene-1,3-dicarbonitriles as green corrosioninhibitor for mild steel in 1 M HCl: Electrochemical, thermodynamic,surface and quantum chemical investigation, J. Taiwan Inst. Chem. Eng.49 (2015) 229-239—each incorporated herein by reference in theirentirety.

Potentiodynamic Polarization Measurements

Potentiodynamic polarization study was carried out in absence andpresence of different concentrations of gelatin to understand the effectof the gelatin inhibitor on the anodic oxidative metallic dissolutionand cathodic reductive hydrogen evolution. FIG. 5 shows thepotentiodynamic polarization curves for mild steel in absence andpresence gelatin inhibitor. Inhibitor efficiency was evaluated fromcorrosion current densities utilizing equation (8).

$\begin{matrix}{{{{IE}({PDP})}\%} = \left( {1 - \frac{I_{corr}^{I}}{I_{corr}^{B}}} \right)} & (8)\end{matrix}$

where I_(corr) ^(B) is the corrosion current density in blank andI_(corr) ^(I) is corrosion current density with an inhibitor present.

The values electrochemical parameters, such as corrosion potential(E_(corr)), corrosion current density (i_(corr)), anodic and cathodicTafel slopes (βa, βc) given in Table 4 were obtained by extrapolatingTafel slopes to E_(corr). The corrosion current densities for bothanodic and cathodic half reactions were significantly reduced in thepresence of the gelatin inhibit as it can be seen in FIG. 5 and Table 4.This is an indication that the gelatin inhibitor successfully inhibitedboth the anodic dissolution of the carbon steel and cathodic evolutionof hydrogen. See C. Zhang, H. Duan, J. Zhao, Synergistic inhibitioneffect of imidazoline derivative and L-cysteine on carbon steelcorrosion in a CO2-saturated brine solution, Corros. Sci. 112 (2016)160-169; J. Zhao, H. Duan, R. Jiang, Synergistic corrosion inhibitioneffect of quinoline quaternary ammonium salt and Gemini surfactant inH₂S and C₀₂ saturated brine solution, Corros. Sci. 91 (2015)108-119—each incorporated herein by reference in their entirety. Nodefinitive trend in shift of E_(corr) in the presence of the differentgelatin concentration was observed, suggesting that gelatin is amixed-type inhibitor. See M. A. Hegazy, M. Abdallah, H. Ahmed, Novelcationic gemini surfactants as corrosion inhibitors for carbon steelpipelines, Corros. Sci. 52 (2010) 2897-2904—incorporated herein byreference in its entirety. Though, the E_(corr) tends towards morenegative in the presence of gelatin and that the βc values were moreaffected as compare to the βa suggesting that the gelatin predominantlyact as a cathodic type indicator. See C. Verma, M. A. Quraishi, L. O.Olasunkanmi, E. E. Ebenso, L-Proline-promoted synthesis of2-amino-4-arylquinoline-3-carbonitriles as sustainable corrosioninhibitors for mild steel in 1 M HCl: Experimental and computationalstudies, RSC Adv. 5 (2015) 85417-85430—incorporated herein by referencein its entirety. A significant decrease in I_(corr) values was observedin the presence of gelatin compared to the blank 15% HCl, and thisdecrease prevails with increasing gelatin concentration. Thus, gelatinreduces the corrosion rate of carbon steel. The decrease in values ofI_(corr) in presence of gelatin can be attributed to the blocking of theactive sites present on the metallic surface. See F. Bentiss, M.Lebrini, H. Vezin, M. Lagrenee, Experimental and theoretical study of3-pyridyl-substituted 1,2,4-thiadiazole and 1,3,4-thiadiazole ascorrosion inhibitors of mild steel in acidic media, Mater. Chem. Phys.87 (2004) 18-23—incorporated herein by reference in its entirety.

Linear Polarization Resistance (LPR) Measurement

Linear polarization resistance measurement was also employed to evaluatecorrosion inhibition efficiency of gelatin for the carbon steel in 15%HCl. LPR is a non-destructive technique and allows for the measurementof corrosion rates in real time. To ensure accurate measurement and nosignificant or permanent disruption of the corrosion process, asufficiently small polarization voltage value of 10 mV was chosen withinwhich the linear relationship between E/I and Icorr holds. See L. O.Olasunkanmi, I. B. Obot, M. M. Kabanda, E. E. Ebenso, SomeQuinoxalin-6-yl Derivatives as Corrosion Inhibitors for Mild Steel inHydrochloric Acid: Experimental and Theoretical Studies, J. Phys. Chem.C. 119 (2015) 16004-16019; S. G. Millard, D. Law, J. H. Bungey, J.Cairns, Environmental influences on linear polarisation corrosion ratemeasurement in reinforced concrete, NDT E Int. 34 (2001) 409-417—eachincorporated herein by reference in their entirety. The polarizationresistance (R_(p)) and percentage inhibition efficiency (% IE) valuesobtained from this technique in the absence and presence of differentconcentrations of gelatin are given in Table 4. The percentageinhibition efficiency of gelatin was calculated using equation 9:

$\begin{matrix}{{{IE}\%} = \left( {1 - \frac{R_{p}^{o}}{R_{p}}} \right)} & (9)\end{matrix}$

where R_(p) ^(o) and R_(p) are values of the polarization resistances inthe absence and presence of gelatin. See S. A. Umoren, Polypropyleneglycol: A novel corrosion inhibitor for ×60 pipeline steel in 15% HClsolution, J. Mol. Liq. 219 (2016) 946-958—incorporated herein byreference in its entirety.As given in Table 4, significant increase and decrease in R_(p) valuesand corrosion rates, respectively, were observed in the presence ofgelatin, indicating the gelatin to be a good inhibitor for the carbonsteel corrosion in 15% HCl. The R_(p) value increases while thecorrosion rates decreases with increasing gelatin concentrations. Theinhibition efficiency was found to increase with increasingconcentration of gelatin. The highest gelatin concentration (2.5% w/v)showed an inhibition efficiency of 88.35% (Table 4). This trend is ingood agreement with that of the weight loss, EIS and PDP measurements.

TABLE 4 Potentiodynamic polarization (PDP) and linear polarizationresistance (LPR) parameters for X60 carbon steel in 15% HCl in theabsence and presence of different gelatin concentrations at 25° C. PDPmethod LPR method Concn of E_(corr) R_(p) gelatin (mV vs. I_(corr) β_(a)β_(c) CR IE (Ω CR IE (w/v %) Ag/AgCl) (μA/cm²) (mV/dec) (mV/dec) (mpy)(%) cm²) (mpy) (%) Blank −401 1030 85.90 124.7 301.0 — 21.86 348.3 — 0.5−428 498 101.4 164.9 145.6 51.65 52.51 145.0 58.37 1.5 −421 354 94.90182.2 103.4 65.63 68.63 110.9 68.15 2.5 −411 329 223.8 409.0 96.23 68.06187.7 40.57 88.35

SEM/EDX

FIGS. 6A-6D show the surface morphology of carbon steel coupons afterimmersion in 15% HCl, in 15% HCl with gelatin, 15% HCl with gelatininhibitor in the presence of KI additive and before immersion andpolished carbon steel, respectively. The SEM micrographs were taken toprove the inhibition of gelatin on carbon steel corrosion in the acidsolution. FIG. 6A shows an uneven surface with large number of rustsdistributed over the surface in the uninhibited acid solution. Thedegradation was considerably decreased in the presence of gelatin (FIG.6B) which shows a smoother and more even surface for the inhibited acidsolution. It has been reported that a smoother surface morphology is asa result of protective layer formation by adsorbed inhibitor molecules.See S. Karim, C. M. Mustafa, M. Assaduzzaman, M. Islam, Effect ofnitrite ion on corrosion inhibition of mild steel in simulated coolingwater, Chem. Eng. Res. Bull. 14 (2010) 87-91; D. Jayaperumal, Effects ofalcohol-based inhibitors on corrosion of mild steel in hydrochloricacid, Mater. Chem. Phys. 119 (2010) 478-484; U. F. Ekanem, S. A. Umoren,I. I. Udousoro, A. P. Udoh, Inhibition of mild steel corrosion in HClusing pineapple leaves (Ananas comosus L.) extract, J. Mater. Sci. 45(2010) 5558-5566—each incorporated herein by reference in theirentirety. In the presence of KI additives in the inhibited acidsolution, a more uniform, smoother, and brighter surface morphologycould be seen (FIG. 6C). This demonstrates a higher adsorption of thegelatin molecules in the presence of KI additive and further explainsthe higher corrosion inhibition efficiency of gelatin in the presence ofKI additive. Therefore, the addition of the gelatin inhibitor reducesthe corrosion that occurs in the free acid solution. Energy dispersiveX-ray analysis (EDX) technique was utilized to extract informationregarding the nature of the protective films form. The EDX spectra ofX60 carbon steel before and after 24 h immersion in 15% HCl in theabsence and presence of gelatin are given in FIGS. 7A-7D. Thecharacteristics iron peak intensity of the carbon steel surface beforeimmersion in 15% HCl (FIG. 7A) was observed to decrease drasticallyafter 24 h immersion in 15% HCl without the gelatin inhibitor (FIG. 7B).A higher iron peak intensity than that of the blank 15% HCl was observedin the presence of gelatin inhibitor (Table 6, FIGS. 7C and 7D). Theweight % of the polished X60 carbon steel surface decreased from about95% to 62.18% with high chloride content of 7.32% and oxygen content of27.73% (Table 5) when immersed in 15% HCl without the gelatin inhibitorfor 24 hours, indicating corrosion of the metal surface by the corrosivemedia (15% HCl). A drastic decrease in chloride content was observed inthe presence of the gelatin and gelatin with KI (Table 5), indicatingthe shielding of the iron surface from the corrosive chloride ion. Thegelatin inhibitor shields the metal surface by forming a protective filmon the metal surface. An additional nitrogen peaks was observed in thepresence of the gelatin inhibitor (FIGS. 7C and 7D), indicating that thegelatin inhibitor adsorbed on the metal surface through an interactionbetween the nitrogen atom of gelatin and the metal surface to form ametal/gelatin complex on the metal surface.

ATR-FTIR

The formation of the protective layer containing gelatin on the X60steel surface was further confirmed by comparing the ATR-FTIR spectrumof pure gelatin (FIG. 8 , line a) with that adsorbed on carbon steelimmersed in 15% HCl with 2.5% w/v gelatin (FIG. 8 , line b) and with2.5% gelatin and 0.05% KI adsorbed on carbon steel in 15% HCl (FIG. 8 ,line c). As shown in FIG. 9 , the ATR-FTIR spectra of both the X60surface immersed in 15% HCl with 2.5% gelatin and in 15% HCl with 2.5%gelatin and 0.05% KI are similar to that of the pure gelatin, anindication of the adsorption of the gelatin on the carbon steel surface.The characteristics amide groups (—CO—NH—) are the main absorption bandof gelatin. For the pure gelatin (FIG. 8 , line a), the most intenseband found at 1635 cm-1 is assigned to the C═O stretching vibration ofthe amide groups. See A. Pal, S. Dey, D. Sukul, Effect of temperature onadsorption and corrosion inhibition characteristics of gelatin on mildsteel in hydrochloric acid medium, Res. Chem. Intermed. 42 (2016)4531-4549; J. Hossan, M. A. Gafur, M. R. Kadir, M. Mainul, Preparationand Characterization of Gelatin-Hydroxyapatite Composite for Bone TissueEngineering, Int. J. Eng. Technol. 14 (2014) 24-32—each incorporatedherein by reference in their entirety. The band at 1334 cm⁻¹ isattributed to the carboxyl C═O wagging vibration of the proline residue.The amide N—H stretching vibration is ascribed to the broad banddistributed at 3289 and a weak band at 3066 cm⁻¹ in consistent toprevious reported N—H stretching of pure gelatin. A band at 1522 cm⁻¹was assigned to the amide N—H scissoring vibration. See J. Hossan, M. A.Gafur, M. R. Kadir, M. Mainul, Preparation and Characterization ofGelatin-Hydroxyapatite Composite for Bone Tissue Engineering, Int. J.Eng. Technol. 14 (2014) 24-32; K. Haruna, T. A. Saleh, J. Al Thagfi, A.A. Al-Saadi, Structural properties, vibrational spectra andsurface-enhanced Raman scattering of 2,4,6-trichloro- andtribromoanilines: A comparative study, J. Mol. Struct. 1121 (2016)7-15—each incorporated herein by reference in their entirety. The bandsat 2933 and 2870 cm⁻¹ are assigned to the aliphatic C—H asymmetric andsymmetric vibrations respectively. See A. Pal, S. Dey, D. Sukul, Effectof temperature on adsorption and corrosion inhibition characteristics ofgelatin on mild steel in hydrochloric acid medium, Res. Chem. Intermed.42 (2016) 4531-4549—incorporated herein by reference in its entirety.For the ATR-FTIR spectrum of X60 steel immersed in 15% HCl with 2.5%gelatin, the band intensities were found to be lower than that of puregelatin (FIG. 8 , line b). The carboxyl C═O wagging vibration wasshifted to a lower frequency (1319 cm-1), indicating the formation of abond between the carboxyl ion and the metal surface. See A. Boskey, N.Pleshko Camacho, FT-IR imaging of native and tissue-engineered bone andcartilage, Biomaterials. 28 (2007) 2465-2478—incorporated herein byreference in its entirety. The amide N—H stretching vibrations bandswere shifted to higher frequencies broad band at 3370 cm⁻¹ and a weakband at 3131 cm⁻¹. The amide C═O stretching vibration was shifted tohigher frequency at 1644 cm⁻¹ and the aliphatic C—H antisymmetric andsymmetric bands were shifted to lower frequencies at 2924 and 2852 cm⁻¹respectively. The above observations suggest adsorption of the gelatinmolecules on the carbon steel surface through the amide groups of theprotein chain. A higher characteristics band intensities and lessershift in frequency from the pure gelatin spectra was observed for theATR-FTIR spectrum of the X60 steel surface immersed in 15% HCl in thepresence of 2.5% gelatin+0.05% KI (FIG. 8 , line c). This explains thegreater adsorption of the gelatin on the carbon steel surface in thepresence of KI which explains the greater inhibition efficiency in thepresence of KI.

TABLE 5 Elemental composition of the X60 carbon steel specimen beforeand after immersion in 15% HCl in the absence and presence of gelatin at25° C. Mirror X60 X60 immersed X60 immersed polished immersed in 2.5 w/v% in 2.5 w/v % of X60 steel in blask of gelatin gelatin + KI Element Wt% Wt % Wt % Wt % Fe 98.54 62.18 65.73 66.53 C  0.93  2.40  9.16  8.81 Si 0.53  0.38  0.30  0.16 O — 27.73 21.54 22.90 Cl —  7.32  1.84  0.99 N ——  1.32  0.61

UV-Visible Spectroscopy

The UV-Visible absorption spectra shown in FIG. 9 , reveals that afterimmersion of the mild steel coupon, the absorption band obtained in theUV-visible region shifted to a lower absorbance value. A behavior thathas been ascribed to a possible interaction between Fe²⁺ and theinhibitor molecules in the inhibited solution. See M. Finsgar, J.Jackson, Application of corrosion inhibitors for steels in acidic mediafor the oil and gas industry: A review, Corros. Sci. 86 (2014)17-41—incorporated herein by reference in its entirety. This can beexplained to be due to some electronic transitions, like as n→π or n→π*(involving the non-bonding electrons of the gelatin O and N atoms) andthe formation of a surface complex between the metal surface and theinhibitor molecules. See S. Karim, C. M. Mustafa, M. Assaduzzaman, M.Islam, Effect of nitrite ion on corrosion inhibition of mild steel insimulated cooling water, Chem. Eng. Res. Bull. 14 (2010)87-91—incorporated herein by reference in its entirety. The formedcomplex acts as the adsorbed protective film that directly reduces theacid attack on the metal surface.

Mechanism of Inhibition of Gelatin on Carbon Steel

The inhibition mechanism of carbon steel corrosion in HCl solution bygelatin could be explained by adsorption of the gelatin molecules on themetal surface. This adsorption of the gelatin molecules on the metalsurface can be via physical (physisorption), chemical (chemisorption) orboth processes as illustrated in FIG. 10 . The nitrogen atoms of thegelatin molecules may exist as protonated species in the 15% HCl. Theseprotonated nitrogens in the polypeptide chain might get adsorbed topreviously adsorbed chloride ion on the carbon steel surface through anelectrostatic interaction (physisorption). See L. Guo, G. Ye, I. B.Obot, X. Li, X. Shen, W. Shi, X. Zheng, Synergistic Effect of PotassiumIodide with L-Tryptophane on the Corrosion Inhibition of Mild Steel: ACombined Electrochemical and Theoretical Study, Int. J. Electrochem.Sci. 12 (2017) 166-177; H. Lgaz, R. Salghi, K. Subrahmanya Bhat, A.Chaouiki, Shubhalaxmi, S. Jodeh, Correlated experimental and theoreticalstudy on inhibition behavior of novel quinoline derivatives for thecorrosion of mild steel in hydrochloric acid solution, J. Mol. Liq. 244(2017) 154-168—each incorporated herein by reference in their entirety.This reduces the evolution of hydrogen which is the predominant cathodicprocess of corrosion in acidic medium, and hence reduces dissolution ofiron. The gelatin molecules may adsorb on the metal surface via donationof lone electrons pairs of N and O atoms to the empty d-orbital of Featoms/ions to form an adsorbed layer of gelatin molecules on the neutraliron surface (Equation 10) or a protective Fe²⁺Gelatin_((ads)) complex(Equation 11) on the iron surface (chemisorption), which inhibits theanodic dissolution reaction. See L. Guo, G. Ye, I. B. Obot, X. Li, X.Shen, W. Shi, X. Zheng, Synergistic Effect of Potassium Iodide withL-Tryptophane on the Corrosion Inhibition of Mild Steel: A CombinedElectrochemical and Theoretical Study, Int. J. Electrochem. Sci. 12(2017) 166-177—incorporated herein by reference in its entirety.

Fe_((s))+Gelatin→Fe: Gelatin_((ads))  (10)

10Fe_((soln)) ²⁺+Gelatin→Fe²⁺: Gelatin_((s))  (11)

Thus, the corrosion inhibition efficacy of gelatin for X60 carbon steelin 15% HCl simulating oil well acidizing environment was investigatedand (i) the gelatin shows high inhibition efficiency for the carbonsteel in 15% HCl at 25° C. and the inhibition efficiency increases withincreasing gelatin concentration; (ii) the inhibition efficienciesobtained from weight loss measurements are comparable with thoseobtained from EIS, PDP, and LPR measurements; (iii) the gelatin acts asa mixed-type inhibitor, inhibiting both the anodic dissolution of thecarbon steel and cathodic evolution of hydrogen; (iv) the gelatinmolecules suppress the dissolution of the carbon steel by formingmetal/gelatin complex. This complex adsorbed on the metal surface andeffectively blocks the steel surface from being attack by the corrosivemedia; and (v) the SEM-EDX, ATR-FTIR and UV-Visible spectroscopicanalysis reveal the gelatin molecules adsorbed on the metal surfacethrough an interaction between the nitrogen and oxygen atoms and themetal surface to form the metal/gelatin complex on the metal surface.

1. Acid stimulation method with downhole corrosion inhibition in an oiland gas well in a subterranean geological formation, comprising:injecting an acidic treatment fluid into the oil and gas well throughmetal tubing to react with and/or dissolve rock of the subterraneangeological formation; then fracturing the rock; wherein the acidictreatment fluid is an aqueous solution comprising (i) a corrosioninhibitor composition comprising gelatin and an intensifier selectedfrom the group consisting of CuI, KL and formic acid, and (ii) 14 to 16wt. % of HCl, based on a total weight of the acidic treatment fluid,wherein the gelatin is present in the acidic treatment fluid in aconcentration of 0.5 to 2.5 wt. % per total volume of the acidictreatment fluid, wherein the intensifier is present in the acidictreatment fluid in a concentration in a range of from 0.01 to 0.05 wt %per total volume of the acidic treatment fluid, wherein the gelatin hasa Bloom number in a range of from 50 to less than 220, and wherein thegelatin has free carboxyl groups in a range of from 78 to 115 mmol per100 g of protein.
 2. (canceled)
 3. The method of claim 1, wherein thegelatin is Type A gelatin derived from acid-cured porcine skin.
 4. Themethod of claim 1, wherein the gelatin is Type B gelatin derived fromlime-cured bovine skin.
 5. The method of claim 1, wherein the gelatin isType A or Type B gelatin derived from fish skin or fish scales.
 6. Themethod of claim 1, wherein the gelatin has a Bloom number in a range offrom 150 to less than
 220. 7. (canceled)
 8. The method of claim 1,wherein the free carboxyl groups in the gelatin are present in a rangeof from 78 to 80 mmol per 100 g of protein.
 9. The method of claim 1,wherein the free carboxyl groups in the gelatin are present in a rangeof from 100 to 115 mmol per 100 g of protein.
 10. (canceled)
 11. Themethod of claim 1, wherein the intensifier is KI.
 12. The method ofclaim 1, wherein the corrosion inhibitor composition is substantiallyfree of a cinnamaldehyde compound, an alkoxylated fatty amine, animidazoline compound, and a carboxylic acid compound having 1 to 12carbon atoms or an ester or salt thereof.
 13. (canceled)
 14. The methodof claim 1, wherein the acidic treatment fluid is substantially free ofa polysaccharide, a synthetic polymer, a quaternary ammonium surfactant,and an organic solvent.
 15. (canceled)
 16. The method of claim 1,wherein the is HCl in the acidic treatment fluid comprises 14 to 15 wt.% HCl.
 17. The method of claim 1, wherein the oil and gas well istreated with the acidic treatment fluid at a temperature in a range offrom 25 to 180° C.
 18. The method of claim 1, wherein the metal tubingis carbon steel.
 19. The method of claim 1, which has a corrosioninhibition efficiency of 55 to 85%.
 20. The method of claim 1, wherein acorrosion rate of the metal tubing is from 12 to 36 mils penetration peryear (mpy).